baby momma drama..

So my husbands daughters mom calls and says she is leaving her husband.... well she said this 2 years ago as well and the first time was around Christmas and we tried to be as supportive and help as much as possible. She is crazy but we wanted to make sure that the daughter had a good Christmas at both houses so she didn't know things weren't good. So she took us being nice and supportive to the wrong level! My husband does most of the communication with her over text and a few calls and some how she put it in her own head that he was leaving me and our twin boys to be with her. She went all around town telling mutual "friends/acquaintances" so of course it got back to us!! So now I'm having to tell my husband to be careful what he says because she is already calling and being super weird nice again after just a day. Me and my husband are happy and he absolutely dispises her because she had their daughter at 26 weeks and while the daughter was in the hospital she was at the bar and told people she LOST the baby so my husband assumed she did until 99 days after being in the hospital and baby girl can come home so THEN she announces to the world about the baby on facebook and then he has to get DNA done to make sure. So he basically cannot stand her for taking away the birth of his daughter and leaving her in a hospital alone (we know she was alone because our twins were born at the same hospital and they remember his daughter and said that mom was never there and never mentioned a dad). We want to be able to help so his daughter doesn't see so much of what's going on but I don't want her going back around town starting rumors like last time. I've tried to get along with her but she talks to my face like a friend and then talks bad behind my back and to the daughter. Me and the daughter used to have an amazing relationship ive been with my husband since she was 1 1/2 and she's almost 5 now but she drills it in her daughters head that I'm not her mom and basically doesn't have to listen to me etc. ugh!! Should I try to reach out and be nice through this situation or just stand back and let it play out? I still care for the daughter the same as my own when she's at my house but I've had to stand back on things that involve important decisions on like school and things like that or discipline I don't handle either. That's for her dad to do.  Opinions? Or similar situations?