Jackson Brothers -- Debbie Rowe Already Abandoned Her Kids Once

Michael Jackson's brothers are refusing to allow Debbie Rowe to wrestle guardianship of Prince and Paris from the kids' grandma -- at least if they can help it -- telling TMZ, Debbie abandoned her kids for cash after they were born ... and hasn't cared about them since.

Tito, Randy, Jermaine, and Jackie tell us, "[The children] are well loved and well taken care of. We are quite taken back [sic] that Ms. Rowe has decided now to enter their lives, after she abandoned her children many years ago for money."

The brothers are referring to Debbie agreeing to give MJ full custody of Prince and Paris after giving birth to them ... in exchange for a lump sum of money.

The brothers insist the Jackson family -- Katherine included -- wants only the best for Prince and Paris, adding, "Our only desire is to see our niece and nephews continue to go on with happy, healthy and safe lives. We will do everything and anything with in our power to help make that happen."