Whether Katherine Jackson will get to raise the kids may begin to be determined at a hearing Monday.
However, one family law expert said Michael Jackson's will is not the last word on who eventually will get custody.
"Legally, its not a binding pronouncement by Michael Jackson," said Michael J. Kretzmer, a family law attorney. "You cannot [act] like you could with a piece of property or a car, or a boat, or a piece of jewelry. You can't give your kids away. You can't bind the court. In part, that's because kids are wholly different in nature. They're not property. You have always got to look out for the best interest of the children when you're in the court."
To that end, one of the keys may be Katherine Jackson's physical vitality.
"The lawyer for Katherine is going to go into court and is going to do her very best to tell the court why Katherine is the very best, the person best suited to care for these kids," Kretzmer said.
Katherine Jackson's lawyer, he said, likely will cover "what her relationship has been, what her knowledge of kids is, what the skills to being [a] parent are, that she has the energy, capability, and stamina to keep up with three kids who are 12, 11, and 5."
Today, the mayor of Gary, Ind., said Joe Jackson will be among those at another memorial scheduled for Friday in Michael Jackson's hometown.
Joe Jackson admitted to ABC News that he has been "very demanding" with his sons and their show business dreams. But he added no one could doubt the key role he played in molding his children into the Jackson 5, and shaping the talent of Michael Jackson, the young star who would become an international sensation.
ABC News' Michael S. James contributed to this report.