family issues. please, I need some advice

Okay I'm going to explain this the best I can and someone please help me, because I'm at my breaking point. My husband and I and our 3 year old daughter had to move in with my grandmother for the time being because we having issues with housing.im also in the first trimester of my second pregnancy.  Well my grandmother is basically raising my cousin (as she  did with me also, mother doesn't care) so she's always here too (she's 4) and does anybody have that aunt that never shuts up and is always a bitch? No? Oh well I guess it's just me. But she thinks EVERYTHING under the sun is her business and he son is a complete and total crybaby. I understand sensitive kids, but no he cries over everything and he's almost 8. But my problem is, before we moved in here, our daughter was a good child. Always listened, never backtalked, was an all around awesome kid. But now she acts just like the other two, she hits me and yells at me, constantly backtalks, doesn't listen at all. And I disipline my kid. The other two NEVER get in trouble because they are angels and do no wrong.(the 4yrold) is always yelling and screaming and hitting people and back talking and now my daughter is acting just like her, along with the constant crybaby like the 7 yr old. My aunt always acts like I never displine my child and always leaves smartass remarks when I do disiplone (whip her, take away toys, time out) and I tell her straight up. You have no right to speak to me about my child when those two do whatever they want with nothing done to them. I'm pregnant, I'm emotional, and honestly about to deck her in the mouth. MY CHILD WOULD HAVE NEVER STARTED ACTING THIS WAY IF SHE WASNT AROUND THOSE TWO. I wish we never would've have moved it. PLEASE TELL ME HOW TO HANDLE THIS