The first one looks like my Buff Orp / Americana X (Hen is Buff Orp / Rooster is Americana). Some of my chicks are very light, some are buff but some are darker like this one.
I noticed in your post you said sometimes you just find some of your chicks dead. My mother hen hatched 9 chicks and they are about 8 weeks old now. I have had them separated from the rest of the chickens in a pen in the barn. I have fresh water, food and a heat lamp during night and early...