I asked this before, but think any answers were lost in the mix... Thoughts and opinions on disc brake adapters for frames without disc brake mountings. I saw some through Busettii(???), but attempts to contact them have not been fruitful.The website seems to focus on electric assist bikes, so these may not even be what I think they are (the adapters).
Will these things hold up, especially under tandem loads?
I would suggest reviewing if your frame has the necessary chainstay clearance required for a rotor. Most disc ready frames take that clearance into account by shaping the chainstay accordingly. Then, perhaps look at having the dropout replaced with one that includes a disc mount.