Janet, Tito, Jermaine, Rebbie and Randy Jackson have fired off a letter to the current executors of Michael Jackson's estate, John Branca and John McClain, demanding they resign from their positions because they've "failed to perform" their duties.

In the three page letter, the Jackson family claim that the two attorneys have not only failed at their executor duties, but have also "taken advantage of a grieving mother and family."

The letter states that after Michael passed, Mr. Branca told 82-year-old Katherine Jackson: "I am Michael Jackson now."

The family's letter goes on to accuse the two lawyers of knowing that Michael's signature on the will is fraudulent. The Jacksons say Michael was not in California at the time the will was signed ... which was on July 7, 2002. Furthermore, the letter says Michael's siblings have evidence to back up their claims.

Branca and McClain have yet to respond. Click thru to read the entire letter.