Did you inherit stacks of 2.85mm filament with the printers? If so, I’d probably get the mini working to burn through it. If it still has the “mini” single extruder, give it the Aerostruder (if you weren’t lucky enough to get one with one), and flash the Marlin 2.0.0.144 Mini w/ Aerostruder firmware NO-LCD or with LCD and run that with the 4.13.8 version of CuraLE (details here). Once you’ve exhausted all your 2.85mm filament with the Mini, you can decide whether it’s worth it to convert to a 1.75mm toolhead. If you did not receive any 2.85mm filament, you can do a conversion of the Aerostruder to 1.75mm details here, most of which apply to the Dual Extruder, but cross over to the single aerostruder (just make sure you get the correct mirrored/standard parts. IIRC, the Aerostruder v1 is not mirrored).
For the Taz6, since it’s already in need of fixing, I’d upgrade… but keep in mind that while they’re very robust and reliable, they are slow. What’s your budget for getting it up? If you can handle configuring Marlin yourself, and source clones of name-brand parts from aliexpress, you can easily get it running with silent steppers, BLTouch, dual z axis control, 1.75mm dual-geared toolhead and more for around $200. Even at that low price, you need to ask yourself if you wouldn’t be better off with something like a Bambu A1 mini.