aries2756:
Why would you HAVE to support your child if he makes the wrong choice? If you do, how will they and their children learn from their mistakes?
And if the parents don’t feel the child is ready to raise a family (not specificly money, but also maturity), then let them not pay for the wedding, or support his shidduch dating.
If you don’t want to punish the grandchildren, place money in a conditional trust that is given to them if they do what you want (either going to Brisk or Yale (or maybe both)).