Help! what should i do? PLEASE?

Ok so this is a tricky situation but my husband and I have been married since oct 2010 and now we have a baby ob the way (I'm due in jan 2012) we just moved outta our apt n march and into our house we r doing well with the bills and rent.we struggle from time to time but we always wrk it out.so my problem is that my husbands mother and her two young sons (my husbands lil bros) want to move in with us.it is only a two bedroom house.we have our room and the room beside ours which is going to be the nursery and its already getting filled with baby items (crib/clothes/toys etc).and I have my attic but it is full of my husbands mother's belongings because this used to be her house.she moved out in feb and then my husband and I moved into it in March after having been approved by the landlord.wen we moved in in march TONS of her stuff was still here that she hadn't taken when she moved.we put it all in our two sheds (both still full of her stuff as of rite now) and we put the rest of her stuff in our attic (still full as well).now she wants to move in with us for a while with the two boys because she wants to break up with her boyfriend and get outta their house and leave him with it on his own.I just cannot handle even thinking about it the stress is killing me which is not good Since I'm pregnant.the whole family is pressureing us to say yes and to help her and she probably wont quit bugging til she gets her way.the pressure/guilt is so much on me.there's absolutely no space here for 3 extra ppl and all their stuff wen they still got stuff here they never took in the first place.we love her to death and feel very responsible to help her as she has helped us before but she acts very childish and never makes smart decisions.I feel like my husband n I have a family our own on the way that we need to worry about and we don't need to be worried about her problems when she is a forty year old woman with a good income capable of helpin herself.shud we say yes or no??????????