Advice~If 2 friends you know are fighting.

You have to be patient and think of a way that both your friends can agree to disagree. Not everyone likes the same things. Maybe try and help your friends remember how well they can get along. Life is too short to be miserable and possibly destroying friendship you've had for ages.

Sometimes people need to except their faults in self and others before they fall out.

It can be hard to not try and take a side but they are your friends and if you go for one side for the other might not like you anymore. It can be seen as childish/immature but, its the way the world works.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If the friends are fighting over a boy/girl they both have a crush on then that is a whole other story.

You have to make them realize that they became friends because they have similar interests and the person they like/fancy is another one of the common interests.
It is perfectly natural for many people to be in love with or be a huge fan of a celebrity. Look at how many teen girls love One Direction for example.

Until one of them asks the person out, neither of them will know if the guy/girl actually fancies them at all. Your friends need to not let the crush come between what used to be a great friendship and still can be if, they come to an understanding that getting in a relationship with another isn't going to take over their life and time will be made for hanging out together.
I know the whole idea of the crush you have being taken away from you by your friend can lead to JEALOUSY. You have three options here:
1- Neither of the friends go out with the guy.
2- wait for the guy to ask either out and in mean time you can both enjoy a common interest.
3- Be happy for the one who gets with the crush. Then go find another to be your next relationship. 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

A fight/argument will finish eventually. Getting involved can sometimes make the argument go on for longer. I suggest being there for both of them and try and show them how they once were brilliant friends.
If they ask for help I think getting them to own up for their wrongs and be the bigger person before damage is done and friendship lost.
Name calling and insulting each other during a disagreement only makes the fire bigger. It's like adding another log to the fire.
I mean it will make the argument go on for longer.

In short, don't take sides, don't get involved with the facts of the argument unless you have clear evidence that one friend is wrong. Also be patient while showing your friends how they actually once got along really great. Could be by looking through old photos, reminiscing about past or going out together and trying to have a good time.  

If you read this and want help on another problem please contact the blog or comment bellow. 
Hope I've helped people with this bit of writing.