Help my baby kittys are dying!

Please help me! My cat, shes an outside cat because my dad has allergies, just had her first litter of kittens. She had four of them. One of them was dead when I found them. She and her babies are now inside. Another of them was VERY weak. I thought he was dead, but when I wrapped him in a warm towel he slowly came back to life. His back foot started turning purple and unfortunately, that one passed away also. I did everything I could. I was such a mess when it happened. I don't think I can take another dying, they're like my own. I took them to the vet and he gave my cat a hormone shot and a tranqulizer. I have gotten absolutely no sleep this week. The two left were always very strong. The one has now started nursing on his own. The other kitten will suck when I hold him up to her. But, he's just getting so skinny! I can see him latched on to her nipple, and he's sucking but when he gets off of her, there's no milk around it. When the other kitten gets done there's milk everywhere. I don't know maybe he's not sucking hard enough. He's gotten very weak like the second one now. I have started giving him kitten formula in a syringe (he won't take it out of a bottle) but he does not want it at all. He will take usually half of the syringe. I try to feed him about every 2-4 hours. I still let him try to nurse from his mother also, just in case he is getting any milk. But now, when I went to stimualte him to go to the bathroom I noticed he was bleeding from his rectum! I don't know what to do. I'm so sad I don't want another one to die. My vet said there is nothing I can do but keep him warm and keep trying to feed him. The momma cat keeps moving the healthy one away from the one that's bleeding. Should I let her do this? I feel bad for the sick one because he is all alone and cries. Someone please help me! There has to be something that I can do! They are about 5 days old now. If someone could let me know ASAP before something happens to this one!

Oh,I'm so sorry! Sometimes these things happen and there just isn't anything you can do. If the little one is bleeding like that,it's probably from some sort of birth defect. It sounds like you are doing and have done all you can for them. Hopefully someone else more experienced can give you more helpful advice. (ETA) If it were me,I'd just snuggle him and love him,and do exactly what you've been doing.