Re: 4 week old kittens with lots of questions!
The pee-ing part is just a natural reaction for right now, they will grow out of that when they mature. Abby is probably getting tired of being a mom and is begining the weaning process, part of which I think is to feed the kittens less milk so they will be hungry when she presents them with other foods to eat. Canned adult cat food is okay until your payday as long as they are still getting some nursing time from Abby.
The Iams kitten food is (IMO) more suited for already weaned (bigger) kittens than for ones transitioning from milk to kitten foods. I would try to find a kitten food with much smaller kibble and no corners, edges or triangles. Rounded and small is the best shape for them.
I wanted to add, I've always used a clumping cat litter for all of my cats/kittens and I've never had a problem, though I have read where some people have had a problem with kittens eating it. When I fostered, I always kept them (mother and kittens) in a bathroom with a sleeping area, food, water and the litterbox in the bottom of my shower, which has a low edge for kittens to be able to get in/out so they could follow mom into the box and see where she 'goes'. Kittens learn very fast how to use a litterbox, though they are a little messy at first. You could also use a shallow tray and towels, just washing and replacing the towels every day. It means a lot of laundry, though...
I wanted to add something else, too.
I would not feed those tiny kittens any of the 'shredded' canned foods. I think some of the pieces may be too large for their tiny mouths/teeth to handle. Feed the 'pate' type of canned food, just mash it up around the edges of a plate, and/or add some water to it to make it mushy and easy for them to eat and lap up. See how they like to eat it, try it regular first and if they have some difficulty, add a little bit of water when mashing it.
Tip: Place a large towel on the floor and the plate in the center so any spills will be on the towel and you can use the towel corners to clean the kittens feet and faces.