Aggressive lap do I get them ready for baby?

I have two chiweeinies. One is a little over a year and the other will be a year in June. They are very protective and have gotten more aggressive about it since I've been pregnant. Also, I moved in with my mom and I think all the "new people" are adding to their nasty behavior. My baby is due in early June and I'm worried about how they'll do with her. They're used to being "the babies" and I don't want them to lash out. What can I do to make it an easier transition?