The multiple chainrings in front would suggest that this is either a homemade tandem built from non-tandem parts.
Or they damaged/lost the original front cranks and replaced it with a non-tandem crankset from a single bike.
Either way they didn't bother to remove the extra chainrings which are pointless on the captains crank in front.
Additionally there is an odd chain tensioner rather than an eccentric front bracket. Cannot tell if that is home made or not.
Are you looking to purchase this tandem?
If so I would ask for the full history on the bike as well as the serial number which is normally stamped on the bottom bracket shell. That might give you some clues as to make/model/year.