Yes. You can leave your assets in trust, with the income and principal to be used as needed for the education of your grandchildren. You can also provide that after the last grandchild has been educated, the remaining principal is to be given to your grandchildren. If you were to pass the excess to your children, there would be generation-skipping transfer tax consequences.
Absolutely. The ability to accomplish this is one of the great benefits of leaving property to your children in trust. By leaving property to your son in trust, rather than through an outright distribution, you can specify that he has use of the property during his lifetime and that, when he dies, it passes according to your instructions to your descendants.