It is not the son in law that supports the family, it is the children help support their old parents. Sin Sod is not set up to support the parents, and it is mostly set at the grooms ability to pay and is a show of good faith. If the folks are ni need then they usually sell some land, either to the kids or just for money. We have bought land from my mother in law. If it is a farang then he usually is in a better shape to give a little more than the other kids if there is a need, but is not a rule of custom. And Sin Sod is generally returned, so has nothing to do with lasting need.