The litter tray thing does work - i had one or two going in a corner and inside the kittening pen! (i leave it out as they use it as a trampoline as it's a soft one LOL) SO small litter tray went into the corner and i white vinegar'd the inside of the kitten pen and put a large tray in there x
Also after every meal i picked ever single one of the kittens up and popped them in trays and scratched their feet in it so they got the idea xx

a few days later and this had cured the problems xx

hope you get them sorted xx

__________________