Late 70's (?) Schwinn Twinn (kinda rusty)
 

This included fenders but I had to take the fenders and wheels off to get it in my car so I didn't reattach them before taking the picture. Best I can find it's from the late 70's. It's a single speed.

These sell for $150 and less in LA - often offered for free. $250 for really nice older ones. Tandems seem to be a tough sell.

Well good thing I didn't pay much for it then 😅

Tandems around here (Pittsburgh) seem to go for around $250 for most, not often lower than $150 from what I've seen.

Being a lesser 1 speed in this condition I would say $150 or so. I would consider this one more of a display lawn ornament bike than a rider. The clunky rear coaster brake can make these tough to ride for more than a short distance on flat ground.

Rusty, crusty tandem = no value in my market. So far, I've lost $$ on every tandem I have picked up.

Paid $4 recently for a vintage tandem, and I paid too much. Hoping to make a few dollars on this one, to break the trend.

Working on tandems can be a PITA.

Now in your case, the pedals alone could be a win. The Twinn cranksets have value too. Or ride it to obtain maximum value.