Welcome to SR!
Ditto what everyone above me says. I am a recovering crack addict and because I no longer wanted the chaos that goes with that addiction, I left behind my XABF. I was stolen from countless times, bailed him out of jail, only to watch him go straight back to crack.
I can understand that it's hard, but if he is not forced to deal with the consequences of stealing this time, I can assure you he will do it again and it will only get worse.
I heard "I'll get a job....I'll straighten up...I'll never do this again" so many times, it's sickening. The one time he was honest, he told me "of course I told you that....I'll tell you whatever you want to hear to get what I want". He has been doing this for 25+ years and has no intention of stopping...EXCEPT when he's in jail and is forced to be clean.
I truly feel for you and your in-laws. But as someone who's been on the "other side", cushioning his fall (not prosecuting) is only giving him reason to do more of the same. I often feel that my XABF is going to be killed when he steals from the wrong person....he would be better off in jail.
Hugs and prayers!
Amy