I have not done RO but some of my "discus friends" did. They often used a trash can(s) for WCs filled w/RO (or otherwise pretreated water, peat moss, Prime, aeration, etc) or had a "dedicated" sink available nearby, RO is not a "pretty", usually 3+ x 1 foot long filter "units" or more (a powder room or laundry sink is helpful). They often had a small water pump to get the trashcan water to tank. I know basements aren't "usual" in CA but that's how some hid the cans/RO back east, maybe a garage? With a place to hang the hose...I use a Python for tap refills, be sure any hose is "food safe", not all garden hoses are.
I am guessing your wife's plants are phyllodendron of some kind (spelling?). Pothos is very similar to "heart leaf" phyllodendron, pothos is usually variegated green & yellow/white,; heart leaf solid green...both ~3-4 inch leaves. It can be pretty but I try to keep sun away from my tanks (algae)...so they may not get enough light. Temporary cuttings might work if you or your wife has a "mother plant" or other sunny area for the cuttings to recoup (window sill?). Can't hurt to try them, they may help a lot...or just a bit.
As for your fish getting distressed from large WCs, I did have issues with dissolved gases in winter...on the east coast. I have seen a little bit of that since moving west but not like there. There were sometimes tiny bubbles that "stuck" on my discus but only in winter. I haven't kept discus on the west (left) coast...different water, different issues. A large change in TDS (total dissolved solids) can be stressful too. (look it up, I'm tired of typing ATM, lol).
Trust discuspaul, wesleydunder, & more experienced (& both at simplydiscus.com, & others there & here), I have discus experience exactly 3 or 4 times... only once successfully over 35+ years of fish keeping. ..But many years of happy fishing keeping, discus are different! They need special care.
I haven't kept knifefish either, I know they like a hiding spot...that may need be on your vac central area! Dead spots in your tank (tubes, under logs) can amass crud that needs removal. Each tank is different...as is each keeper & their abilities to provide for these
You know, we'd like to see pics of your tank, we might be able to offer better advice then.