You might consider getting a lawyer & talking to him/her if you don't already have one.
You might want to consider removing your e-mail address for your protection from trolls etc. who frequent forums.
You are an adult since you are 18. You & Your Father could end up with problems you don't want if you go against the aunt's wishes. A minor doesn't get to decide where she (or he) will live.
You said the oldest granddaughter was taken from your home & is with the Father. Do you still have the other children? Is there any reason why the Father should not have his daughter?
First off - she needs to stop shoplifting.
She should go to court & plead not guilty. Since she has no income, she should ask for a public defender & discuss with him/her what her options are.
You didn't say how old you are. If you are a minor, tell (talk to) your parents. If you're not a minor, then read the links above in order to understand a civil demand & to help you decide whether to pay.