M.T.
Hi K.,
Congratulations on the new baby. It is very normal for a 2 year old to be demanding of mommy when there is a new baby. I wouldn't respond to the shrieking, but I would pay her extra attention. When you know it's going to be feeding or diaper time soon, pay her some attention first. Let her know you're giving her lunch first, and feeding the baby second, or diapering her first and the baby is last. My daughter was older, 4 years old, when her brother was born but at times he would fuss and I'd be in the middle of something with my daughter. If he wasn't really crying but just fussing, I'd say so my daughter could hear, "You need to wait a couple of minutes, I'm busy with Kayleigh right now." Let your daughter know when she comes first. Pay her extra attention at a time that you're not tending to baby. Have a special basket of toys and things that only come out when you're feeding or bathing the baby. Good luck with the sibling issues
As for the stepdaughter, you said that she very rarely sees her father. If they rarely see each other, I'm not surprised that she doesn't see him as someone to respect, and she barely gets to see him and he has 3 other girls that he lives with. That must feel awful. If he rarely sees her, then he isn't raising her, and there is little control he can have (and less that you can have) over her. I would encourage visiting as much as possible, but if you're afraid of the effect she would have on your girls, the visits should be just her and dad, or when you are at home, or when your girls are not home. I'm sure that she would be appreciative of some time alone with dad - it probably feels bad to her that your girls have him all the time, and even when she's with him, she has to share him.
Good luck!