Inappropriate or whatever, this is already a drama-infused situation. By injecting yourself, you'll do nothing but increase the level of drama. They'll be talking about you and they'll be talking about how you don't want them to talk to each other and who do you think you are telling them whom they can and cannot talk to. This is catty stuff. As a dude, it's best to ignore it for the most part and be careful what you share with you step mom from now on.