As you'll find in about 13 years this is normal for teenagers and you can beat your head against a wall trying to change it. Or not. Beating your head that is. You've been around this forum for years so you are aware of disengaging but perhaps need a refresher course. I've linked a article below.

With your own child you'd want to stay in the fray but since you'll gather none of the blame nor credit for how these kids turn out why don't you let Daddy deal with them. In fact considering your condition why don't you stop doing everything for the kids. No cooking or clean up after they leave. Time for new mommy to let someone else pitch in so let Daddy do it all.

By the time baby is here and past infancy he'll be kinda in the habit of doing it all meanwhile you can spend your time concentrating on the one kid you can take the credit for.

http://steptogether.org/disengaging.html

I'm starting to think these men are all defective…blah!

The problem with disengaging and leaving it all to be a mess is you can't have lack of hygiene when you have a newborn on the premises. Thus you just have to get the tidying and cleaning done for the next few years. I vote for those advising that this should be "not by you". The problem with the option of leaving Dad to be their maid is that Dad will possibly continue to operate that role model with your own child, which is bad parenting and you don't want it in your own setup. He needs to change his ways now if only for the sake of your child together. But also for yours and your skids', for if the guy continues to behave like this then you will have entitled adult skids in due course who continue to abuse his hospitality -- I know, I have one. It's dreadful to behold. So my advice is, put it straight to the skids -- not that they have to help out now as a baby is on the way, that would make for resentments of the baby -- but that they have reached an age where they must help both their Dad and you with various regular chores. I personally taught my then teenage SS to spring clean a bathroom thoroughly from top to bottom -- with all the products,all the equipment etc. I made it like I was teaching him a life skill but the aim was that that would be his chore whenever he came on fortnightly visits. He loved it actually, and finally got to understand how adults feel when kids muss up the housework they have just done. Problem for me with that was that shortly after that event, BM stopped the kids coming so often so it was not ingrained into his bones like I would have wanted. But it's a method that did appear to work at the time.

"How do I deal with my step kids not helping with basic household stuff?"

Oh, been there and done that, lady!!!!!!!!!!!!!!!!!!

The only thing you can do is make a list of things you want the skids to do for themselves and take it to the DH. It's the Dh's job (says my counselor) to make the skids do things. Otherwise you set yourself up to be the "evil step-mother".

If Dh has a set of balls, which is very rare, he will see to it that these chores get done.
The skids will still know it came from you, but you wont be the one harping on them about it.
Dh should just explain to them that they are not living in a full service hotel and they minimally should be cleaning up after themselves.
Have Dh pay them a small allowance, and if they refuse to do their work, take away something they like.

Back before counseling, I was the evil step-mother because I REFUSED to wait on SD (or BD for that matter) like I'm some kind of a hired hand. So I got the stomping and slamming and bad attitude. Bullsh*t! So I made a chore list for each kid and when the skid didn't do the chores on hers, neither did I and the place became filthy and I didn't care.
So me and DH would bicker about it.
All B.S. This is your Dh's department and he needs to deal with it!!

When I moved in with DH his sons (and him) were nasty pigs. When we moved his couch to move out we found the missing turtle, dead as a nail. They left dishes, trash, clothes everywhere. Could not get the boys to do anything! DH had been a single father and it was, literally, pure survival. BM was never one for cleaning anyway, so they never learned. SS21 is still a slob, when he spends the night with SS17 he leaves trash and clothes around. SS19 and his GF are so messy we had to tell them to move out because we worked all day, and came home to a trashed house and a hungry granddaughter. With SS17 I have had to teach him to take dishes to the sink, pick up clothes and wet towels off the bathroom floor, and throw trash away. BUT he is a teenage boy and he still needs to be told to do things. His current chores are taking out the trash, taking the can to the curb, cleaning (term used loosely) his bathroom, and mowing the lawn once a week. One thing I have learned to do is to NOT pick up after him. His dad will come home and see it and HE gets on to him. The boys tend to deny ownership of things that they do not want to put away, so those orphans go in the trash. If I come home to a mess I turn the breaker to his room off to turn off the playstation. He cleans up fast. If he doesn't mow the lawn we take his phone away. Then his playstation, then his TV. Then he has to mow the lawn and pull weeds. He's slowly coming around..

OMG...I seriously thought I was reading my own post. I am going through the exact same thing. Except my SS are 16 and 18! So sorry to let you down but I'm sure that doesn't give you much hope. I am also expecting a baby in September and I really worry that things are going to go to the dogs around my house if I'm doing everything. Our counselor told me to stop doing things for them. I don't want to live in a pig pen though...UGH!!!!!!!!!!!!!!!!!!!!