I’m concerned about my mice?? (Are they fighting? Etc)?

I have four female mice in a 10 gal. Tank, plenty of food, plenty of water, with a wheel (which they cover with bedding) and an igloo shaped hide (also covered frequently). I’ve noticed today that one of the four is much bigger than the rest even though she was the same size when I got them, as well as one of my... show more I have four female mice in a 10 gal. Tank, plenty of food, plenty of water, with a wheel (which they cover with bedding) and an igloo shaped hide (also covered frequently).
I’ve noticed today that one of the four is much bigger than the rest even though she was the same size when I got them, as well as one of my other’s seeming to have a bit of redness and what looks to be small splots of blood by her ears.
I can’t tell if the biggest one is picking on the others or hoarding food or what but I am concerned for their safety and would appreciate any tips.
(I have the injured one in a separate 5gal tank until tomorrow; I might resort to separating them into pairs if I have to) Any help is very much appreciated!
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