Yes it is possible for a friend to be more important then your family because if they are really really good friends and they help you with everything and your familey don’t they could be more important then familey, maybe they are like familey.
One of the friends could die to separate a strong friendship or one of then could change and start not to like them.
You can repair such a strong friendship by careing for them and try to change them back to who they really were.