No, females won`t, but males might.
Yes, some rats can live together. There are certain types of rats that dont like to live with each other. If you want 2 rats in the same cage, i would recommend getting 2 rats from the same species. Liek if your going to get a dumbo dwarf rat. You should get another dumbo dwarf so they live good with each other.
Rats fight to establish dominance.
No unless interaction from a male rat (such as getting a rat that is about to have babies). two female rats can not have babies
The behavior that is shown by two bighorn sheep heads in a fight for a female is aggression. The two sheep will fight until one gives up for the female.
2 female Bettas will not fight provided they are in a large enough aquarium.
The males fight for the female. Not usually with the female. In general, the male will harass the female to breed, but not fight with it.
only if there is two males and one female they will fight to mate with the female
If two brothers are kept together from birth it is unlikely that they will fight with any dramatic effects. They will have the occasional scuffle, but this is for dominance and one usually gives in before there is blood shed. In my experience (and i bred rats for the local pet shop for ten years) male rats will not live together too peacefully if they are strangers being introduced to each other after they are about 12 weeks old...although depending on the individual temperament of the rats they may come to tolerate each other. i prefer to keep two male rats together, as opposed to keeping them separate (they are social animals and need company) and i prefer male rats to female rats as they are usually more docile and easier to tame. And there are obvious problems to keeping a male and female rat together. When getting a rat, it is the best option to purchase two brother rats together.
if they are two males it courtship they will fight near or to the death for a female
There are two common causes of wheezing in pet rats or mice. The pet rat or mouse may have caught a cold or either there is dust in the cage from the shavings.
to fight over the female
With or without a dominant fish in the tank two female bettas shouldn't fight. It's only the male of the species that fights.