daughter freaks out asking why you're selling your house, tell them both that you're downsizing to a condo to help them through college. Let that marinate for a while.
If they ask why your home hasn't sold later on, say you discovered radon levels were in the stratosphere and no one would buy it.
Let your daughter and SIL know you called his parents and together started a gofundme to help them out.
That should hopefully get the point across. If it doesn't, take them on a shopping spree. On the way home, stop at a plasma center and ask them to wait while you sell plasma to help cover the cost.
If all the above fails, I'm sorry to say, but your daughter has married a Utah fan.