If you decide to restore this bike - you should (imo) improve the brakes. (By the look of things, the Captain has control of the front brake
only).
IMO, this
is a specialised bike, produced for non-challenging riding. If it were mine, I'd sell it, 'cos it'll require a considerable amount of time and money. Furthermore, it is likely that it'll require further modifying and improving. For example, the chain tension looks as if it will need some attention; the brakes will need improving. I'd also replace the handlebars.
The current gearing and brakes would make it less than ideal for longer rides. It probably would be advisable, not to have two adults on it - most older steel-framed tandems flex dreadfully. If you do want a tandem for two adults to use, on fairly challenging roads, then I'd consider something else.
At the end of the day, it depends what
you wish to do with it. I find that I get a great deal of satisfaction, just in 'doing up' a bike; I've lost money on every one mind.
Your bike would be fine for pootling along quiet country lanes that are fairly flat, with a child or small adult as stoker. It
does have the big advantage, of the front being detachable from the rear - making it easier to transport. (Detachable tandems cost ££££ to buy)