What is the best way to deal with my husbands former wifes(she passed away) adult daughters?

My husband and I have been married for 4 years along with him came 2 adult women he calls daughters. They have caused so many problems for my husband and I over the past 5 years. They have called and asked about our will, they want to know who and what we spend our money on. One of these girls actually had the nerve to slap me once when I tried to tell them that their kids were out of control, of course I defended myself, and my husband took her side. It almost caused a divorce. We went on vacation one year and asked one of the girls to take care of our dogs, well she took it upon herslef to bring her sister over and go through our personal belongins, I found out because one of them told my son when she was drunk and he told us about it. This stuff with these two grown women goes on all the time, then when they get confronted or we do something they don't like they wont speak to us for months . I have tried to do everything in my power just to be their "friend" and have given them so much with out wanting anything in return. They treat my husband terrible and have no respect for either one of us. My husband does not have any children of his own, and raised these two girls from the ages of about 4 and 5. I tried sitting down with them a couple of months ago so we could just let the past go and get along like a normal family. For me it's not working, I don't trust them at all. They are the type to smile at you and pretend that everything is great and turn around and stick a knife in your back. I told my husband I was sorry but I just don't want anything to do with them. It's hard but it's the only way I know how to keep the peace. They just started speaking to us after about a year and half, and in that year and a half we have had nothing but peace and quite no interuptions no drama, it's been fantastic. At this point I feel like I'm caught between a rock and a hard place. I refuse to let these two women ruin what my husband and I have. Where do I go from here?