Who has similar problems with Stepdaughters?

I have five stepdaughters who are 23, 22, 19, 12, & 8. The 12 & 8 yr old come over every Sunday watching everything I say and do, then report to their Mom. Then their Mom yells at my husband about me. I don't really know what is going on. The 12 yr old girl wipes boogers and food on our chairs every Sunday and the 8 yr old tells her Mom AND Dad I smack her, pull her hair, and tell her she's fat and ugly!! I have never said or done anything like that! I'm never alone with them. When they come over they are "acting" aways happy to see me but when I leave the room, the 12 yr old will follow to see what I'm doing, then pretends to want to talk to me about girl stuff. I use to enjoy talking to all of them but they write about me and email to me what they write about me. I've talked to my husband and he has had several talks with them but it gets worse. Their Mother doesn't know me and convinces the youngest I abuse her! I found them snooping in my purse twice! UGH I don't know what to do!