"I think it goes back even further," said Brown. "He had a lot of pressure as a boy, then carrying the group, then being the focal point. It became too much. He let go of more important things in life, his faith. He became a self-worshipper. He let go of his family."
Phoenix, who is still in touch with Jackson's parents and brothers and spoke to Tito just a few weeks ago, said the family would like to celebrate Jackson's milestone birthday with him, but has been unable to reach him. "The family has been trying to get hold of him, it's very hard for them to get in touch with him."
Instead, family members, parents Joe and Katherine and older sister Rebbie, are expected to attend Phoenix's special birthday tribute concert in his hometown of Phoenix. His revue will play its usual mix of Jackson 5, the Jacksons and Jackson's solo hits.
For a while now, the brothers have wanted to reunite with Jackson for a tour. The last one they did together, the Victory Tour, was 24 years ago. A Jacksons tour, Phoenix said, would not only thrill fans but boost the brothers who have struggled financially without Jackson.
But Brown thinks even Jackson touring the way he used to appears to be out of the question. "I don't imagine he's physically capable," he said.
Brown is also doubtful about a new album. "He's been trying to complete an album for a long time," he said. "I think that's within his reach. But will it even really matter? He doesn't even have a record deal. That's what's really amazing. He's in a situation where has to prove himself all over again."
It's a very different situation from his fellow '80s pop icons Prince and Madonna, who also turned 50 earlier this summer.
While Prince and Madonna continue to make hit records, fill stadiums, appear at the Superbowl and on magazine covers, Jackson has become something of a recluse, releasing yet another album rehashing his greatest hits in celebration of his birthday.
"They were on a level playing field for a long time. Then Michael took such a bizarre turn to his life," said Jonathan Cohen, a senior editor at Billboard magazine. "Their careers could not have diverged more."
ABC News' Thea Trachtenberg contributed to this report.