Michael Jackson‘s family is involved in a complex legal battle … and they’re not all on the same side in this one — ’cause MJ’s son Blanket is trying to stop his own grandmother from using estate money in her ongoing fight.

Here’s the deal … Blanket — MJ’s youngest son, whose real name is Bigi Jackson — filed documents this week, obtained by TMZ,  asking the court not to allow his grandmother Katherine to use Michael’s estate money to fund an appeal of a previous ruling.

Basically, Blanket and his grandmother were recently working together to stop the executors of Jackson’s estate from going through with a huge business transaction that they were very much so against.

The docs don’t say exactly what the transaction was — it’s been shrouded in mystery throughout this saga — but, based on recent reporting, it seems like it may be related to the deal the estate made with Sony to sell about half of Michael’s music catalog for $600M.

Blanket explains he and his grandmother presented their arguments opposing the deal … but ultimately the court ruled against them — seemingly bringing the legal issue to a close.

However, Katherine’s decided to appeal the ruling … a move Blanket says he doesn’t want any part of — and, more importantly … he doesn’t want his father’s estate paying for her legal bills. As you know, he’s an heir to the estate … so that cash is pretty important to him.

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The way Blanket explains it in the docs … the appeal has little chance of winning, and he says he doesn’t think it truly benefits the beneficiaries of the trust to continue the fight — so, he simply doesn’t want the estate to foot the bill for it … something Katherine wants.

Blanket’s also asked the court to use its best judgment to grant Katherine reasonable attorney’s fees incurred from the pre-appeal battle — which he agrees she’s entitled to … at least to a certain extent.

It’s unsurprising Blanket’s filing against Katherine … just yesterday, executors of Michael’ estate reportedly claimed that she receives a seven-figure allowance for the year — money Blanket presumably would rather she use for the appeal instead of the estate’s dough

Seems like the family’s not totally seeing eye to eye on this one … a judge has yet to rule.