Help!!!!!!

Ok so last night my sis in law took my two nieces to a gymnastics party what we thought seemed fine it was not she lied said it was free but it wasn’t she had to pay 40 for them to go and later she posted a pic and saying date for one movie for one I wanted quite I got it...( they are living with us I always Had them so I have them more now any ways) ...well she left the six year old in charge of the three year old.. (not to mention my two half nieces and nephew have abandonment issues cuz she never wants to spend time with them and always tries to get away from them she sneaks in the house after work and wears a diaper so she can come out when the two older ones are in bed or she stays out all day I mean it’s much peaceful with out her here ..we had to homeschool them cuz they couldn’t go they where HORRIBLE in school.. (and when we trie to show her all the progress they have made even the kids trie she don’t want to see and she don’t want to hear it)...but back to last night when she posted the pic of her picking them up the three year old looked Terrified and when she came home she wasn’t her self she looked like she just watched a bad horror film but when we went to sleep last night she woke up twice crying and had to get in bed with me and my mom cuz she had a nightmare and kept saying.. I was sad I couldn’t find no body ...the last time she just stayed we didn’t put her back in her bed ...anyways her mom is trying to get a bigger car which they need it was stupid to get such a small van to begin with but when she called my mom picked up the phone (my mom also do their taxes ) but she was calling to see if my mom was done and she said no she didn’t finish giving her everything and when my mom was telling her she was about to take a nap with the three year old cuz of what happens last night ( she told her one the phone ) she said oh yeah I know she’ll get over it and tried to start back up one the car but mom said I gotta go and hung up .....but what hurts me is she didn’t and does not care about nothing she talks down about her kids as well and is rude crude and all idk i just wish I could get full custody if not my brother with no visitation with that women ...does anyone else have prob like this as well and what do u do ...I’m soo upsets I want to scream in her face .....but today the little one has been sad all day today it hurts my heart seeing her like this she’s usually always happy and giddy but today she is not and keeps telling us please nana please come with us to gymnastics next time or aunt Laura I know u will stay......