Selling a Co-Owned Car That Isn’t Paid Off

When I bought my car at the dealership, I had a relative co-sign for me. I am now learning they actually a signed as a co-buyer (even though they too thought they were purely co-signing, and have absolutely no interest in owning the car). I am now looking into selling the car, and my question is does the co-buyer still need to sign off on this even though the bank still has the title? Also is the title in the name of the bank or would it still have our names on it, just the physical location is the bank? Because I’ve read when you have the title in hand, I COULD sell the car so long as our names had an “or” in between them, but I have no idea what happens in this case

Selling a Co-Owned Car That Isn’t Paid Off