Welcome to TDK! I missed your first post, but it sounds like you’re doing great with these little ones ~ kudos to you!! Have you had a chance to take them to the vet yet? They should probably go see a vet at least by six weeks old, sooner if you think there is a problem. I think clay litter is ok; I used it for my babies, at eight weeks, and it’s what they were using in the animal shelter where I got them, too, that’s why I stayed with it. Just make sure the sides of the box are low enough for them to get in and out; at first, you may have to ‘show them’ how to use it…. take your finger and scratch in the clay while they watch, then gently place them in the box, and take one of their little paws and try to help them scratch. It may take a few times, but they will catch on quickly when they are old enough…. Mother Nature and instinct are wonderful things!!!
Please keep us posted on your little darlings! Can you take any pics of them? What are their names? You can set up a catster page for free. Click on my pink name and the page will show you the link to my kitties catster pages. Many of us here have set them up for our cats.