Wow, it sounds like you really have your hands full!
I'm sorry you have lost those kits. I hate to say it, but my experience makes me think that you will probably lose that last kit as well. It's very, very unusual for a single kit to survive, even during warm weather and with the best of care.
It is extremely difficult to hand raise baby rabbits - most experienced rabbit breeders give up even trying. Often, you work so hard just to keep them alive, and just about the time you think they are ready to start eating on their own, they die on you. If the doe is alive and she has milk, you are
always better off getting her to do the work.
These days, I am doing things that I never would have believed possible when I first got into rabbits (about 30 years ago). When possible, I just give the doe a nest box a few days before her litter is due, and leave her alone. Unfortunately, sometimes I can't do that and still have live baby rabbits. Some people say they can raise rabbits outdoors when the temperature is well below freezing, but all I can say is, it doesn't happen here. So if I have a litter due during cool weather, I put the doe and her nest box in a carrier cage, and put the carrier in my hall closet. A lot of people will tell you that if you disturb a doe enough, she will kill or abandon her litter, and that certainly can happen, but most of my does have gone ahead and had the babies, cleaned them up, pulled fur, etc, just like they are supposed to.
Sometimes a doe gets everything else right, but doesn't seem to know that she needs to nurse her kits. I always check on my litters at least once per day. If I notice that a new litter doesn't seem to have been fed, I put the nest box in a carrier that is only slightly larger than it is, put the doe in the nest box, and close the carrier. Most of the time, the babies find the doe, and she feeds them. Most of the time, I have only had to do this a couple times before the doe figures out what she needs to do. Every once in a while, I will have a doe that simply wants nothing to do with her kits, or doesn't have any milk; that is why I breed several does to kindle at the same time, to have at least one more rabbit for "backup" in case something goes wrong.
Another thing I do, is to keep the nest box in the closet during cool weather. Early in the morning and again at about sundown, I take the box out and put it in the mother's cage. Most of my does just hop right in and feed the kits, but I stick around just to make sure. If the doe doesn't get in the box within a few minutes, I do the carrier bit. Once the babies have been fed, back to the closet they go. I can usually do this up until they are about 2 weeks old, by which time, they are furry and mobile enough to safely leave with their mothers.
I don't know if anything I do will be of any help to you, but maybe my set up will give you an idea of something that can work out better for you next time around.