People do say Guys for groups of men or women, but A guy is usually male.

Most generic animal terms are the specific term for the male, thus dog is generic, bitch is specifically female. Some have enough terms that there is a generic, a specific male, and a specific female (horse, stallion/gelding, mare; yea even unto the next generation - foal=baby/child, colt=boy, filly=girl). Cattle are the only ones generically referred to by the specific term for the female - cows.

ANY animal that has sex, doesn't mate for life (and even then...) and has more than one offspring/pregnancy can have different fathers for the different offspring. You can have sex with three guys (male ones), have triplets, and each can have a different father.

Off topic: you (women) can have twins (or more) that are identical on your side and fraternal on their father's/fathers' - single egg splits and the daughter cells are subsequently fertilized. These can then still have different fathers, if you are fast (in any sense you want)!