First of all - I've managed to be more poor than my in-laws. So that's never been an issue.

I did co-sign on a used car loan with my son post mission when he had no credit. But it was a small enough loan that I wasn't worried about it and figured I could take over the car if I needed to - it's since long been paid off.

Quite honestly - I've given money to family and friends but never loaned it to them. Not sure what I'd do in the circumstances you describe - the amounts I'm talking about are small enough that gifting it made more sense than working out loan details. I have no idea what I'd do if there was ever a family member in real need beyond what I could give them without getting it back.