I have a guinea pig question?

Have they got a big enough cage? - sometimes they become a little territorial when their cage is smaller as they don't get enough personal space. If trying a larger cage doesn't work, you should separate them before there is an injury (bites can turn to abscesses).

This is very common when one female is in heat, I have never been able to figure out just which one it is but usually in 2 to 3 days all is back to normal. You may go through this every 16 days or you may skip a heat cycle, it just depends on them and what is happening at the time.As long as there is not actually fighting and blood being drawn you have nothing to worry about and it is very very rare for females to fight to that degree.

maybe they were fighting over food or space. Try getting a bigger cage or making sure they have enough food. I think they are fine if they keep doing it a lot lot((say 4 nights in a row)). Then i would suggest putting them in seperate cages.

I would be safe and put them in separate cages.