In new legal docs, obtained by TMZ, Elijah and his wife, Marieangela King, lay out the reasons why he doesn't need his mom to step in as conservator of his estate ... and he’s taking shots at Cher and leveling some pretty serious accusations in the process.

Elijah claims he's now sober, paying his bills and is committed to managing the quarterly payments he gets from the trust set up by his late father, legendary musician Greg Allman.

As we reported ... Cher claims she's concerned her son has substance abuse and mental health problems and can't manage the money he gets from the trust ... but here he says that's just not true.

Elijah's wife goes a step further in the docs ... alleging Cher essentially orchestrated a kidnapping of Elijah and had him held at a Mexican rehab facility against his will.

In the docs, Marieangela claims Elijah was brought to Mexico in October and told by a doctor Cher hired that he would be doing holistic alternative therapy ... but she claims it was actually a "makeshift prison-type facility known as the 'Baja Rehab' where he was being held against his will."

Marieangela claims she traveled daily from L.A. County to Rosarito "to rescue Elijah from the captivity his mother arranged." She says Elijah "was held captive" there for 2 months until Mexican federal agents escorted him out and dropped him off at the border.

For her part, Cher has vehemently denied the kidnapping allegations.

Elijah's wife also takes some shots at Cher in the docs ... she says she's known Cher for 11 years and says the singer is "categorically unfit to serve" as Elijah's conservator.

Marieangela claims Cher doesn't drive, doesn't make her own food or dress herself, and has told Marieangela she's "manic depressive."

While Elijah's giving his reasons why he doesn't need a conservatorship, there's a court hearing set for March 6 to determine whether Cher will be appointed conservator anyway.