Pilot reported a TCAS/RA with another commercial jet landing on the parallel Runway which was off course and too close to them.

Narrative

Flight XXXX from ZZZ to DEN we were flying a visual approach to Runway 16R; backed up with the ILS. Just prior to Meryn intersection we encountered a TA alert followed by an RA alert. Looked out my left window and saw Aircraft Y next to us; very close we could see passengers in their windows. The FO complied with the RA and descended as instructed. I then alerted the Tower. The Tower acknowledged the RA and told us they were lined up on Runway 16L. I told the Tower if they were lined up on 16L why would we get an RA alert. I believe they were lined up on the Taxiway to Runway 16R; that's how close they were to us. When clear of conflict was announced they were much further away from us. No other alerts were observed after they lined up properly to their Runway. The Tower during this event seemed uninterested. Aircraft Y not lined up on correct Runway. If pilots would back up there visual approaches with some guidance from an ILS or Localizer it would at least ensure your aircraft was lined up on the correct piece of pavement.