You can do some stupid things when manic but illegal things are not part of bipolar. I have had bipolar most of my life and have spent too much money when manic but I never did anything illegal. Bipolar does not make you steal or break any law. What you do, even though bipolar, is your responsibility. Bipolar is not excuse.

However, this seems to be a pattern behavior (stealing) along with not taking responsibility for one's actions (the whole family) and you are not going to be able to change them. They have to bear the burden of their actions before they will want to change.