Alicia, here’s a very useful web page on how to take care of orphaned kittens.
http://www.peteducation.com/article.cfm?cls=1&cat=1388&articleid=912
The best way I’ve found to get kittens to want to eat is to make sure they get peed & pooped prior to feeding. Do you know how to do this? It involves a clean, warm, damp washcloth being rubbed gently in a circular motion on the anus & genitals. (This is a lot like what the mama kitty does to clean them up.)
If these kittens really are only 4 weeks old, you’ll need to do this for them. It’s absolutely critical. If you don’t get much pee or poop from doing this before they eat, then try it after they eat.
When you start the kittens on wet kitten food, use a saucer, mash down some wet food about 1/4 inch thick across the saucer, and then dribble kitten milk replacer all across the top of it. They should get the hang of it fairly quickly.
As you’re getting them weaned onto kitten food (wet or dry), after they’re done eating, make sure you have a litterbox nearby, one that’s shallow enough for them to step in & out of by themselves. (A cookie sheet works well.) Use either plain clay litter or a wheat/corn/pine based litter, or finely shredded newspaper. Don’t use clumping litter; if they accidentally eat much of that, it will clump in their stomachs and create all kinds of nasty problems.
If you get them started onto dry food, make sure that you have a shallow dish of water available to them at all times.
Oh, and try feeding the runt more frequently than the other kitties. Monitor its intake closely.
Good luck!!