Sister calling police on brother

My mother passed away 4 years ago leaving behind 5 kids,one having special needs. When she died I was suppose to take care of him . My sister agreed to pick him up at the train station , since she works in the city. Then the next I was to pick him up. I called to tell her I was coming after work. She started cursing screaming u don't have any where for him to go I told her I just got this half of house plenty of room lost my deposit on my single apartment because of leaving early .so I was out 1200 dollars had furniture in storge. Then all of a sudden she called started cursing n said. I told him u don't have a place to go n I know u don't want to live in the streets so stay here . She told him all this because every month she would get money. Her atmospher in her house is very bad nothing but cursing smoking pot. People over all hours of the nite n day n he has to sleep on the floor mean while she let's her friend's son live there n give him the bedroom so when social service comes she just moves him out. She can't handle him treats him very bad tells him nobody wanted him so she got stuck with him. Not true. When he moved here from the south he brought a picture of our parents that my ma had since the got married. So I asked him to let me take it n make copies. He went to get it n I took it told him I will bring it back next week. An hour passed n he called me telling me my sister called the police on him (I mention he has special needs) because he gave me the picture which belongs to everyone. But is claiming she had it all her life n I didn't have a right to take it. So she is taking it out on someone who can't defend himself. I know he doesn't want to live there any more cause he told me. He acting out cause the enviorment he is in is not healthy for him. But calling the police, wasn't the right choose . He gave me his social workers name. Should I step in n call her to explain what is going on?