Would surgery to remove a ureter alleviate some flank pain due to double ureters that may be blocked?

Reconstructive surg. Pain associated with a double ureter is due to obstruction or reflux (urine backing up from the bladder due to ureteral valve malfunction) or rarely a yo-yo effect within a y-shaped double ureter. Likely needs reconstruction. Repair + removal needed to bypass the double ureter could be part of the reconstruction. Ask urologist to draw diagram to explain procedure. Get second opinion if concerned.
Possible. If it actually is the cause of obstruction, it may help but no body can assure you of that. Also if the nature of the obstruction is expected to hurt the kidney function then there is another reason for surgery besides just only relieving pain.