Quinton Aaron‘s recovering in the hospital from a spinal stroke, but his family says the woman who is by his side and making medical decisions for him is fibbing about being his wife … though she begs to differ.

The actor’s brother, Jarred Aaron, tells TMZ … the woman claiming to be his wife, Margarita Aaron, is actually married to another man. His immediate worry is she’s misrepresenting herself as his legal wife to the medical staff at the hospital and is helping to make “crucial and life-saving medical decisions.”

Margarita tells us … she and Aaron “got spiritually married.”

She adds … she does NOT have power of attorney, and has never made medical decisions on Quinton’s behalf.

Jarred isn’t buying that, saying … “I genuinely fear for my brother’s life.”

Margarita says, “If he’s saying I’m such a bad person, why does he live with me and Quinton?” In response, Jarred says he didn’t know they weren’t legally married when they all lived under the same roof.

Quinton, by all accounts, has not been confronted with these claims … his brother says he’s not telling Quinton yet, and is going to wait until he makes a full recovery from the spinal stroke his family says he suffered.

Still, Jarred says … “I have all this crucial information that Quinton doesn’t know about and now it feels like I’ve gotten it too late.”

Quinton’s family tells us in a new statement … “Since the health crisis of our beloved family member Quinton Aaron, we have raised some suspicions about the legitimacy of Quinton & Margarita’s ‘marriage’ to each other as well as her legitimacy as a registered nurse.”

The family adds … “We have found some alarming details. We as a family believe Margarita isn’t who she claimed to be to us. This has caused us to want to investigate her further.”