My sister was recently remanded in prison. Should I be the only one helping when we've other family members?

Be there for her. Put yourself in her shoes. Would you like her to be there for you? Or would you like to be all alone? No one needs to be alone at a time like this. After all, God doesn't look down at her, so why should anyone else look down at her? And God is the only one that really matters. You are doing the right thing!