I've hand weened 2 litters of orphaned kittens, the last were 10 days old when their mom disappeared (only one had eyes still shut). The first one did not have a BM until they were close to 3 weeks old, and the last one waited until about 5 days later.
A couple of things that worked very well for us:
We kept them in a stereo-size box on the floor with a lot of towels in the bottom to keep them warm. We covered most of the top with a towel to keep the sunlight and drafts out. It seemed to calm them. Once they decided they wanted out, we created a boxed in area about 5X5 with heavy throw rugs and towels, expanding the area larger and larger while their inquisitiveness and physical abilities grew.
We started feeding them every 4 hours, then slowly worked to twice daily (once they were eating a lot on their own). We spoiled them so much that they didn't get off the bottle until they were close to 8 weeks old.
We sat on the floor with towels on our laps to feed them. They didn't take to bottles, so we used syringes for the purpose. We would rub their backs to burp them, but typically the handling we gave them with their post feeding bath stimulated a burp. If after bathing they hadn't burped, we held them up against our chest and lightly tapped their backs.
We kept washclothes in a bowl of warm water after feedings. Rinsed the water out thoroughly and wiped their entire body from head to rump after each feeding. It was this spring, and pretty warm in May so we didn't worry to much about drafts when they were wet. They were messy eaters and we always had to wipe off the excess KRM. For their rumps, we started with a dry towel (they always peed first), then switched to the damp to clean them off and stimulate their BM. When they started peeing without stimulation on a regular basis (about 4 weeks), we started using toilet paper and holding them over a litter box. By 5 weeks they were trying to use the litter box on their own. We did have to show them to lift their tails away from their body when they used the litter box.
The early poops are really hard on them. You would expect them to be very runny, but some were as firm as a healthy adult cats. It really hurt them, and they will grunt, squint, meowl and make all kinds of noises. A little disconcerting at first. They didn't BM every day to start....sometimes skipped a day or 2 between the first week.
We kept them away from all the other cats until they were fully weened, then only introduced them one cat at a time.
There is a better orphan kitty site out there, and will continue to look for it. I read it after I had weaned the last litter and found that I did almost everything as they suggested. Here is one that at a glance, appears to be pretty good.http://www.feralcat.com/raising.html
Good luck! You are an angel for doing this!
btw....Scarlett, Muddy and Koko are the 3 that we kept from the 2 litters we weaned. They are absolutely wonderful babies and worth every minute of it.