Maybe you should tell them that they trigger you and it's best to stay at a distance. Sometimes you just have to take care of yourself. Toxic relationships are not healthy for anyone involved. So tell them, out of respect for everyone, it may be best not to have visits for a while. Some people don't understand this, but after the abuse from your mom and how it seems your sister doesn't have understanding for your situation, it may be best to take a break from them.