I'll try to keep it brief. DH has always had a somewhat tricky relationship with his father. FIL means well but is a rubbish communicator and can be very abrasive, if not outright bullying. In recent years their relationship has improved tremendously, but FIL likes to gift us money as a way of controlling us- influencing our lives. We were happy to accept money when we were expecting our DC, as SIL had received the same amount when she had DC. He wanted to give us money for a house deposit for Christmas in 2016. When we tried to politely refuse on the grounds that we don't want his money we wouldn't be able to save any money ourselves so felt bad taking it, he got very annoyed and insisted we should accept anyway. Then 18 months ago I wrote our car off in a stupid parking accident (no one was hurt and it was incredibly unfortunate the car had to be written off). FIL insisted on buying us a new car, but also insisted he wanted to have a say in which one. DH agreed without speaking to me about it. He put me down, lectured us on the need to be financially responsible (seemed to think my dad had paid for our car and we still owed him for it, which was nonsense) and was horrid to his wife the entire day. The whole experience left me feeling rotten and humiliated.
Yesterday, DH was involved in a car accident for which the other party was entirely to blame. FIL has already been enquiring about the car and whether it can be repaired. Neither I nor DH want him to buy a new car if our current one is written off. Tellingly, DH said "I hope he doesn't offer to buy a new car". I said we can say no, but it is very difficult. FIL is visiting this Friday because they're in the area anyway, and I have a strong suspicion there will be an offer of (money for) a new car. When I've asked DH what he is going to say if this happens, he deflects the issue by saying things like FIL won't offer before we've heard from the insurance or that we won't know whether the car is being written off by then. I am not convinced by this at all, and FIL is quite dominant in conversation and you easily find yourself agreeing to things without having had a chance to think them through. Annoyingly, we don't have much money going spare, which means the money would come in handy. It just always comes with strings attached and FIL is offended if you try to refuse it (he's very wealthy and I think he is used to money getting him what he wants). So, long story short: how do we say no, given that FIL knows we can't really afford a new car and will be annoyed if we don't want his money, and the history of him domineering us.