How tight should the tandem front chain be?
The sync chains should always be tight enough that they're not physically capable of falling off, and there shouldn't be any easily perceptible droop, ideally in any rotational position. If you pull the chain up and down, it should have a little bit of flex and "give" to it, the feeling of the pins having some aggregate movement to give in their inner plate bushings. Some sources like to give specific amounts of free movement that indicate a properly tensioned chain, but this is the wrong approach because it depends on the length and the internal clearances of the chain. Too tight is when you can feel any binding or extra friction. Sometimes parts with poor concentricity or damage force compromises where there may be some spots with slight binding/friction. On a nicer bike like this one would hope not, but it's not the end of the world.

Incorrect chainline will encourage dropping in a sync/singlespeed chain capable of it. But mostly the right answer is the chain shouldn't be capable of it, and if it is then problems are likely.