Not really sure what to do
So my boyfriend and I have been together for two years. I have a 5 year old and he has a 5 year old and we also have a 7 month old together. His 5 year old daughter does not listen to me AT ALL. I went over to my bf’s moms house today with both of my daughters and I told her many times not to pick her sister up and she kept trying to and one of the times she ended up picking her up and she dropped my 7 month old baby. Luckily she didn’t get hurt but it made me so sad. I then told her not to give her baby sister any yogurt and she pretended to put the yogurt spoon in her mouth by touching her lips with it. Right in front of me!! As we were walking out the door she took her sock off and through it at my 5 year old daughter face and my daughter said why would you do that? My daughter started to tear up and then my step daughter started laughing and snickering at her :(. She is a bully to my daughter and when ever she doesn’t get what she wants she has a HUGE fit and she is constantly doing a whining cry fit thing. She doesn’t share. She gives everyone an evil look if she isn’t getting her way and slams doors and screams.