If you want two of your friends to be friends, they have to get along. Two of my friends whom I hang out with all of my precious time do not seem keen to eachother whenever we are all together. I would like to understand why this is so, and why it's so difficult for them to just like eachother! For cripe's sake! I have good taste in friends, so why can't they like the other good pickin's who are on the same boat as them? There can be a few causes for such problem to occur.
One problem why they do not like eachother could be the fact that they have different tastes and opinions. One thing that one friend may like can tick off the other. Some dividing opinions may even lead to feeling offended or angry with the other. Different tastes can also be hard to mix because there is less to converse about when getting to know eachother.
Another problem may be that they do not know eachother very well! You cannot expect people to magically bond with eachother when they have no time to do so. You may want to leave your two friends some time to hang out on their own without you around for comfortable bonding.
They may also not like eachother because they have behavioral issues and social unawareness. Some people do not have very fine social skills and may have trouble getting to know people. They should find some courage and confidence in themselves to speak and interact with eachother. Hopefully then there will not be indifference or awkward silence.