I'm sorry but this might be quite a long one. I'm a regular poster but have NC.
My dm has been married for about 15 years now. She didn't live with her "d"h until after they married because they didn't live in the same country. At first he was very charming and seemed to really care about me and my dsis. However soon after he moved in his true colours began to show. In fact within 24 hours of moving in with us he had a huge argument with my dm and threw a lamp at her head. My room was next door so having heard everything I ran in to check my dm was ok, I was told by both of them to go back to bed (I was about 14 at the time).
Over the years his treatment of my dm has pretty much been the same, if anything it's probably got worse. He's cheated on her several times, possibly most recently over Christmas. He has been violent towards her (and me and my ds once or twice), is emotionally abusive and constantly gets into debt with credit cards. My dm usually only finds out when she accidently stumbles across credit card statements, he's never honest with her. She once even found he'd obtained credit cards in mine and my ds's name. He pays nothing towards the running of the house and basically lives there free.
Despite all this my dm still defends him and won't kick him out. At first she said it was because she didn't want my db (who is now 12) to grow up without his dad. I can kind of understand that, but he never spends any quality time with his son. He loses his temper with him constantly and during Christmas spent most of his time glued to his phone and ignoring us all. At one point my db picked up his dads phone to play a game on it and my stepdad lost it completely. Obviously hiding something.
I know I can't force my dm to get rid of him but I am genuinely scared for my dm and db's safety. I am convinced my stepdad is a sociopath. He lies about EVERYTHING, even stuff that isn't really important. He doesn't seem to have any empathy at all, whenever he does show emotion it isn't genuine. It's like he's just doing what is expected of him. For example his dad died recently. Literally within hours of him dying my stepdad posted on fb letting everyone know. In the next few days all he talked about was how many likes his status had got and how cool it was. I know people grieve in different ways but he didn't show any sign of being upset. It really scares me what he might be capable of. Whenever he is pulled up on a lie he becomes very aggressive and sometime violent. My dm discovered another possible affair last week and told me she was going to confront him. I'm worried he will hurt her.
Sorry for the lengthy post. I don't know what I want from posting this I just needed to talk to someone, and maybe get some advice on how I can help?