I want the money I leave to my four children to remain in trust for as long as is legally possible. None of them is capable of managing the estate or preserving the investment, so I want them to receive only the income from the invested capital. Can I preserve the estate indefinitely?
It's your money. You can set up a trust that will last for quite a while -- for as long as your children live, if that's really what you want.
However, you'll require some hands-on help from a lawyer to make sure the matter is done right. Consult an experienced attorney who can help you address the many issues of management and funding that will arise with a trust that will exist so far into the future.
For tips on finding the right attorney, read How to Find an Excellent Lawyer.