Tiki, if Tangaroa (I swear, I'll never spell the poor guy's name right; is it Tangora?) is building a bubble nest and seems healthy other than his tail being all melted together, I think I'd probably just let him be. Maybe he has a genetic tail thing that kicked in sometime after you got him.
Fin melt is . . . iffy. I'm not sure it's even a real disease. It's more likely the result of parasites or something like that and I'm not sure, you've tried like every med there is. If one of those didn't work, I dunno.
EDIT: UGH. I left the girls alone in the bathroom while I changed their cage and when I came back, Dinah had gotten on the sink and was busy sucking on the nozzle of my lotion bottle. AGAIN. Second time she has done that. I guess it doesn't hurt her and now her breath smells all lavender-y but still, I worry about her when she does that. It's organic lotion . . .
Eva is wearing the fur off her nose chewing on the bars of her cage. :( I don't know how to stop her though. I even tried hanging toys and things directly in front of the spot where she likes to chew but she just pushed them out of the way.