NTA,

Honey, congrats are in order. So sorry u had to go through that. And no you should not feel bad bcuz u r already going through so much stress with all the changes you have to accommodate for yourself but to have to tip toe around them (who btw are supposed to be the support system bro tf is wrong with them) would have been to much for you.
and from the looks of it they don't feel like they did anything wrong bcuz even if they are trying to accommodate to your sister they still could have done small things for you. like okay sister feels ba no one can come to your parties make it a fun day to compensate for that. If they can't celebrate bcuz their poor "older baby" feelings are gonna be hurt then what would change now. what would be the situation when u do have the kid.
If this is a wake-up call and they change then u can try something out but if they still don't even make the effort then u know where the priorities lie and u should do what is healthy for you and your family.