K.W.
In Law questions are so difficult. When I started my business I borrowed $1800 from my son and his wife was against it. I made sure that I returned the money with interest in 3 months instead of the 6 we agreed upon and have never made that mistake again. Obviously the family dynamics between your husband and in laws are such that anything you say will be seen as controlling or nagging. I would chalk it up to a gift but let your husband know you will not agree to helping them in the future no matter what the deal is.
I would give my mother in law anything she needed, but she wouldn't ask for anything and wouldn't take it if she thought it was making things difficult for us. My husband does so much for my mom, but she wouldn't let him if it caused any problems.
I think the dynamics are the key and your fil is a taker without regard to others consequences. Now you know the ground rules so for the future just say no.
K. @ The Nestingplace