Yes, I get this all the time. They don't acknowledge me at Hello or Goodbye unless I initiate it. Their dad gets a hug. I get nothing, not even "Bye."

Am I invisible?

Yes, me too! My skids shun me, too – it's part of the universal, toxic passive-aggressive skids’ playbook.

Passive-aggressive individuals use this tactic to gain power and provoke negative reactions from their targets. It's a way for them to devalue or control others. In the case of a stepparent, the skids show the stepparent less enthusiastic greetings in public compared with the bio-parent…and when the stepparent informs the bio-parent about this…we look like ‘the crazy one.’ That’s why it’s such an insidious and effective tactic. The skids know instinctively how dense and willfully ignorant their bio-parents are - they count on it - that's why they get away with these shenanigans. 

I counter it by calling it out in front of the bio-parent in a friendly way: “Say, Whittle Johnny, I notice you don’t give me as warm a greeting as you do your bio-parent…”

During school pick-ups, when I was alone with the skid, and the skid ignored me, I didn’t respond. We drive along in silence. After a few times, the skid wanted to talk, and I told her, ' We will talk during dinner’ (when Daddy-cakes is present), so I stopped this skid doing the push-pull with me. My boundary is that we will talk ONLY with your father present during dinner.  If I didn't set this boundary, the skid would make small talk with me only to go full force later at the dinner table, expressing herself in such a way with her Daddy-cakes to make me feel like a stranger and left out.

When someone shows you who they are—THE FIRST TIME—believe them and change your behavior to protect yourself. 

The skids do it to cause tension between you and your spouse because they know that their bio-parent will defend their shenanigans if you call attention to it.  The least you have to do is not let it bother you - don't act like it does. 

So, jerk a knot in some tails and make sure they all are clear that they will be polite and respectful toward you. Period. Dot.

Make sure that DH is clear that he will be on board with enforcing this on the spawn in the home. As your DH, he owes you to keep his failed family weenus lemurs in the polite and respectful zone.

IMHO of course.

And it's something your DH should be addressing with his kids. So, I suggest a "talk" with your DH to address his poor parenting skills.

My own sweet girl did something like this when she was 16...walked into the house where I had several friends sitting at the kitchen table, visiting. She walked past us without saying a word. Before she stepped out of the kitchen, I said, "Excuse me, can you say hello to my freinds?" Embarrassed her but she quickly self corrected, apologized and greeted everyone. Later she told me how embarrassing it was and she'd never do that again. 

For me, it wasn't the skids i was invisible to but my SO's family. I would say hello or try to talk to one of them or help with something and it would be like i just wasn't there. No acknowledgement or reply. Didn't even look up at me. Or would pretend not to speak English even though i had heard them on the phone with my SO dozens of times and all their convos were in English. The first time a cousin spoke to me and actually listened to me speak i was like a TV ghost "You can SEE me?!" 

Everyone is different.  I do think you come off as a bit too sensitive.  Kids should learn to be polite.. and I'm not sure if you aren't saying hello to them.. and they are ignoring you... or if you just "wait" for the greeting.

I mean, by your post, you say you get along ok.. that they are nice enough to you generally.  So, when they come in the room.. say "hi dad".. say "Hi Stepkid 1"  Then if they don't respond you point that out to your SO.. "hey.. I think you should remind kids when they are addressed.. they should be responding to that person".

They may also see you and their dad as a "unit".. greeting him means greeting you.

Not every kid looks at their stepparent as a parent.. they may see them as their parent's partner instead.  but not necessarily 
blood related to them.  Now.. as to gifting.. for you it wasn't enough that there were presents "from them".. (even if facilitated by their dad).. but you wanted to have them delivered in a specific way.  I mean.. they are kids.. they were excited about the ton of things they got.. that's not abnormal.

And the reality is that they may always have this slightly disconnected feeling with you.. and that doesn't mean they hate you.. but it also doesn't mean you have to keep putting your neck out to be chopped off.

I would try to be more engaging with them.. if that's what you want.  Make a point of greeting THEM personally when they come in the room.. before they have a chance to ignore you.  If yoiu say hello.. and they say.. "hi dad".. have another question ready for them.. "hey.. how was school today.. are you still going to the gym on thursday.. I'm planning on spagetti tonight.. does that sound good?"  make them respond "to" you.. maybe eventually they will fall into more of a habit then?

Or disengage... they aren't "your" kids.. as long as they aren't destructive or actively rude or mean.. maybe step back and don't make such efforts to go and buy all the gifts?  let your husband do what HE wants to for his kids.

[ if you don't demand...you will never get ]  even just to break chops 

DH is the bio parent... and he's allowing his kids to disrecept you!   He should have a talk [first thing] explain he will not stand for third disrecpting of any adult in his home. Your his wife, there SM and they must show respect .  
[second ] if this continues, then there will be consequences,   No phone for a day, then two days. 
'BUT this is DH. job and he's not doing it 

Yep, this is 100% what I experienced too all the time. Especially from my younger SD. And I 100% agree with what Toaster says, they do this deliberately. My SDs are 16 (this year) and 18. My DH has to constantly remind them to say hi to me when they just arrived at the house. Sometimes they do, sometimes they don't. He also always has to remind them to say goodbye to me. It is pathetic. To the point where I would do the same to them, if they don't say hi to me then I won't say hi and acknowledge them. It is a very rude behaviour. They don't do this when they come and visit DH's parents, or attend any social gathering. They would always say hi and bye to everyone there. So why do they ignore me? I think it is to show that they don't like me or something, but as Toaster pointed out, it is most likely a power play and to make the stepparent feel less (sub-human) and devalued. 

In my case it gets to the point where my SDs would not invite me to play any sort of board games even though I'm right in front of them. My SD16 would also constantly offer her dad and her sister to try her food (i.e. ice cream, drinks, fries, etc.) but not me. And they would sit right in front me at the dinner table and ask their dad when his birthday is so that they can put it into their phone diary, but not ask me. Or they'd ask dad what his favourite subject at school is, but not me. I can go on and on with this. And not once ever my DH points this behaviour out to them right when they do it. And the problem is if he points it out afterwards, they would usually just deny it (and therefore makes my DH and I look bad, look crazy). 

I, on the other hand, never did that to them. If I offer my DH something, I would offer it to everyone. If I invite one kid to play board game, I would invite the other. And the older they got, the worse this behaviour became. 

After a while and with the benefit of hindsight, I think that this behaviour is a type of social bullying and it is called exclusionary behaviours. Imagine if you did this in your friend's group at school, or at work. If say, you ask everyone to come out for lunch, but on purpose leave out one colleague/friend. This would make them feel so crap, as if they are not liked, and that there is something wrong with them, and that's exactly what these kids are doing.

I agree that your DH should be doing more to correct this behaviour. I disagree with ESMOD saying that this is not a behaviour directed to the stepparent and that she's being sensitive. If this kid can be polite to everyone else, and say hello and bye without being prompted, but they cannot be polite to you, then it is definitely something to be sensitive about. It is definitely a behaviour that is just directed to you. And letting DH ignore this behaviour means letting his kids constantly be rude and letting his kids bully his wife. That is not normal.

Kids, especially those who are older, need to start being held accountable for their actions. Parents shouldn't just ignore and wish these behaviours would go away and that they'll get better with time. They haven't in my case, in fact, they'd gotten worse and I think that DH is all to blame. 

If SK live primly with you. I would demand respect.  They would be grounded with out electronics until they learn.  If EOWE then disengage. Totally. No trips, no going out with them. Or taking them anyplace. Until either they respect you or stop coming over.  You don't need visitation from disrespectful kids. SO  can see his kids at McDonald 

'no reason to try to keep peace in your marriage. Your DH is letting this disrespect to go on. HE in fact is disrespecting you also.  I don't know how you can live this way.