I'm going to call the police/cps on my sister
Are you aware of what will happen once you call the police or cps on your sister?
I will accuse my sister of stealing my computer
You shouldn't call the police or cps on your family for such petty reasons. If the children are taken away from their mother it would break up the family.
I think it's fine for my sister to go away.
You may think that this is funny, but how would you personally feel if someone called the police on you for doing something minor to a family member? Most likely, the police will get you in trouble for filing a false report.