Those are decent rims and they do not appear to be wearing out, provided they are straight when all the spokes are there and properly tensioned.
The usual reason spokes break is because the wheel was initially built with insufficient or uneven spoke tension. If it is a tandem with a few thousand kms, I would expect the spokes to give up eventually even if properly built, however I may be wrong. But if spokes are breaking, replacing all the spokes will make the wheel like new.
ANother option would be to purchase new complete wheels. You may want to consider having the wheels properly tensioned and stress relieved, or doing it yourself, when the wheels are new. Prebuilt wheels are usually built with insufficient or uneven tension and start popping sopkes after a few hundred kms.
Of the wheels on the link you posted, most would not work for one reason or another.
This was the only one I saw that would work. But almost any 8, 9, 10 speed cassette hub 26" wheel will work.