Randy, Jermaine, Janet, Tito and Rebbie Jackson all signed a letter, demanding that the Executors of the MJ Estate step down, claiming the executors are failing so badly, the stress caused Katherine to suffer a stroke.

Sources connected with the Estate are now lashing back, telling TMZ they believe Randy and Jermaine (they are not including the others) are strapped for cash and know when Katherine dies there is no way they can get their hands on a penny of MJ's fortune -- that's because all of the money goes to charity and in trust for Michael's 3 kids.

Our sources believe ... Randy and Jermaine are trying to make it appear that Katherine is infirm and may need a conservatorship. And the sources further believe Randy and Jermaine will try and get themselves appointed as her conservators, which would give them access to more than $70,000 a month.

We know Katherine's people have denied she had a stroke. As for the Estate failing miserably, it seems like bad timing, because new court docs just revealed the Estate has grossed nearly half a billion dollars, wiping out MJ's massive debt.