From your blog I gather your goal is to have a usable tandem with modest upgrades. With that assumption my comments:

Velo Orange bottom bracket should give you reasonable use.

Consider modern brake levers. With modern levers the brakes may stop fine if properly adjusted.

If new brakes needed I would measure the canti stud placement. From picture they seem close together compared to modern placement but that maybe a error on my part. I suggest modern wide proifile canti brakes like Tektro CR720. They work well, not expensive and more in line with the style of the bike than V-Brakes.

Agree with new handlebars and stems.

If you get the rim brakes working you might do without a drum brake.

New Rear derailleur, maybe front as well. Assume you want to keep the freewheel 5 speed for budget purposes.

You mentioned rebuilt or new wheels which sounds good. This is the major expenditure.

New cables and housings all around.

Keep the cranks if they work for you. but as mentioned new chain.

New cogs and chains if needed.

New tires. Tires have a great impact on how a bike rides.

Enjoy working on it.

P.S. a brass bell from Velo Orange would be a nice touch.