I would rotate, not hand feed at this point. Triplets often fight and it may have nothing to do with milk production. Sometimes they fight because one is smaller, sometimes because they are fighting over a nipple. Kit fights will quickly turn deadly. You have no idea how much damage they can do until you actually see the aftermath.
If dad is separate from mom and is in a kit proof cage, then rotate out the largest kit by itself and put it in with dad. Every two hours, switch the two smaller ones and the one bigger one around. If one is really small, then I would leave that one in with mom at all times and rotate out the two bigger ones every two hours. Make sure that the cage that dad is in is kit proof so you don't have a kit escape and die somewhere that you can't find it.
If you don't have dad separate, or his cage isn't kit proof, then you need a kit proof carrier. You will need to place half of the carrier on a heating pad on law, the other half off the heating pad. The kits can move off the heat if it gets too warm this way. Give them something to cuddle up with like a stuffed animal or some fleece. Remember to rotate EVERY TWO HOURS. Set your alarm - that means overnight too.
If you do end up needing to hand feed, which again, I would see if rotation works first, then there is an FAQ under breeding and babies about taking care of kits in the event that mom can't or won't. Read through that and it has all the information you need.