Mrs Zero and I do a lot of songs at open mics. Last night - Hallelujah, Hero, Many rivers to cross.
If you have one other who can do enough vocals to do duets, there's a few others to consider. We do Perfect Day as a duet by one of us singing the first two lines of each verse, then the other the last two. There's the somewhat dark Where the wild roses grow (Kylie and Nick Cave).