For future reference..
you need to go through alot more introduction steps,
AFTER,
going through a long quarantine time.
And with injuries.. Bag balm is great.. I personally wouldn't use liquid skin on a rat much less a hairless but there may be other opinions on this.
And 20 rats in a cage, introduced at different times, is gonna be kinda hard.
Best bet would be to get them all after being weaned, from the same breeder/breeders.. if you want the best chances of them getting along.
I have had 26 rats in a cage,
but they were from two moms I got with that intention.. I bred them together and each had one litter, and I split males and put them with the dad in a 4ft by 2ft cage, and the girls went with the moms in another large cage.
Good luck with your babies.