I Have Guppies, they Seem to fight, is this bad

Right now we have 4 guppies (2 mail and 2 Female, we think) and A female beta living happily in a 20 Gallon tank, there are plenty of plants and fun things for them but still 2 of them swim quite vigorously with each other. We believe that these are the 2 males, the slightly larger of the two has a very spotted tail and flairs it when they are together almost like he is showing off, saying "Ha! Look at my fin, its spottier than yours 'flitter flitter flitter'". The slightly smaller Male is redder and its spots darkening. They do seem to 'fight,' like trying to nip at each other. Why is this? Am I doing something wrong? Is there anything we can do to help them? These fish are only a couple of months old, and as far as we know they have not birthed anything, they were given to us from a neighbor who got them from working at the humane society. If you need any more information I am happy to supply it!

Wow. Is sailortinkitty ever an ignorant fool. Don't listen to a single thing she says.

Ideally, you should have your guppies in a 2:1 female to male ratio. This will prevent dominance in the males (you know, the whole "there are enough chicks for the two of us" kinda male mentality). Look into getting a couple more females.

It may not be that they're being aggressive either. Males are known to get frisky with one another from time to time (I should know - the three males I have in my 55-gallon are, uh, interesting to watch from time to time).