Did you leave all the keets in the incubator until they were dry, fluffy and running around? Sometimes taking them out too soon can cause leg issues, they need the extra humidity and the traction of the wire floor until their legs and feet get working good. If that wasn't the case, then it sounds genetic to me, maybe too many years of inbreeding within the flock that the eggs came from. I'd seek eggs from another source next time just to be on the safe side. Also, those keets that do make it to adulthood and are able to breed may possibly produce keets with the same kinds of problems.
Slipped tendons are painful for the keet, and the longer you wait (and the longer the tendons are slipped out of the groove and the joints swell more) the harder it is to correct it, plus the longer the keet is in pain. If you wait too long the tendon just won't stay in the groove and heal, no matter what you try. If you aren't confident enough to try to correct the problem asap, IMO it would be better to just put the keet down and not let it suffer any longer. I know you mean well and care, but some conditions just aren't fixable after a certain point. Good luck with it.