Honestly not seeing the reason to stay with someone that devalues your feelings and opinions. 

I'd fight fire with fire. "are you depriving my kids of the Christmas they want?"  Smile very sweeetly and say,"Not at all dear, have a wonderful time. I choose to not have my schedule dictated by children and only spend holidays with people I like."

I'd have a real problem with no private area for me. Again, smile sweetly, "Either I can have a private area in the bedroom and bathroom here, or my own apartment."

So what if he gets defensive, stand up for yourself. I agree with simifan - if he wants to go to Arizona and won't agree to do anything else, you go somewhere else for Christmas.

And let him know that your bathroom is now off limits to kids, and is only for you and him.

Honestly, if he can't consider your needs at all, what kind of partner is he? Let him know you are concerned about getting married until these things are worked out.

No need to argue.  In the Christmas example, just respond that you don’t care to go to Arizona and will make other plans. Eventually he will either stop making plans without you, or you’ll realize that you don’t need him around disregarding your wants and needs. 

You have just as much power as he has. Use it. 

Do not marry him, not yet, for a long time. If you can, have your own place.

If there are no other choices, for you right now, then try to have a talk with him. That is your first line of defense.

Tell him that you need to be included in these decisions, have these things discussed with you beforehand.

Let him know that the adults make the decisions, not the children.

Often the parent is defensive because they blameshift (happens to me). Other things are going on that are dysfunctional, and they dont just go away with divorce and/or separation.

This is your household, and you need to take over as the Queen Bee. He sounds very controlling. Saying that you are depriving the children is gaslighting you. This is not a healthy dynamic to be in. And the Gma not treating you well. Well no wonder you dont want to go there. Let them go without you!

Just an FYI - this kind of thing gets worse not better.

Two bathrooms and the children can use both of them? Oh, h*ll no! A woman needs her own bathroom. Tell your SO this is something you are not willing to compromise on and put a lock on the door if needed.

Please, hold off on marriage until you get some of these issues worked out. Your So seems very controlling.

Do not marry someone with kids. Do not marry someone with kids. Do not marry someone with kids. Period. Oh and seeing the update. Do not buy property with someone you aren’t married to. So much no. 

He only acts like this when is regarding kids

Which has ruined, even ended, plenty of marriages.

My SO was/is like this. Always defensive about kids, didn't consult me about things regarding them, even if it involved me. I stand up for myself and push the issue anyway, because it's important enough to me. I told him if I'm not important enough for him to consider my feelings on things that involve me, that's not the kind of relationship I want to be in. Yes it causes fights, but he has changed a lot of things now. He almost always includes me in decisions that involve me. He tells skids to ask me if they want to have a sleepover since I had an issue with him just telling them yes without consulting me. (Ideally he would just ask me first and then tell skids our decision, but I didn't press the issue).

The issues you mentioned are a hill to die on for me- I would not be able to marry someone unless they were addressed and he was willing to compromise.

What kind of help do you want.

Are you looking to get your life back? Do you think you made a huge mistake and need help with getting OUT of it?

When is your wedding date??

How often do they come visit or they actually live with you full time? This is a big problem, my DH does the same thing to me, he will promise his children what they asked for before even talking to me, then when I get upset he said “ oh I didn’t know I need permission from my wife on everything if it’s for my kids” I mean it’s not even permission, it’s called respect. But he will never understood what his problem is. Try to tell him how you feel. Marriages are the two become one businesses so be really careful because his children will never gonna go anyway. Take care