I hope they survive for you, too! Even if they don't, though, you are doing extraordinarily better than anybody else I could think of! Baby mice are VERY difficult to hand-raise. That some aren't making it is really no fault of your own. I know that's little comfort when you see all your hard work not working.
On the subject of birds, unless a bird is endangered or protected (such as a state bird), many rehab places euthanize any that are brought in. If it is a non-native species (such as a European Starling or English sparrow), they are required by law to euthanize it. They're not required by law to tell you this, though. I know a woman who worked in a rehab center in Lexington and she told me that people bring in starlings and sparrows every summer and they euthanize them. The reason they don't generally tell people is that people might also find a bluebird or other native bird with dwindling population and not realize what they have, yet try to hand-raise it because they think the rehab center will euthanize it. I've tried fostering birds before (both domestic and wild) and I failed every single time. The only time I half-way succeeded is when I took part in rearing a baby society finch along with the parents (I took her out of the nest and fed her every couple hours, while they also fed her every other second, it seemed).