This is an odd problem... I am writing four character who are together for quite sometime without encountering anyone and I don't have the problem. But I write out of a clear point of view and describe the others through the eyes of one of the characters. I let that character make the observations.
Hey guys, Thanks for all the replies. I think switching the view point around is a good idea, so I'll try and implement that a lot more. I've just finished the first draft now, so I can go and start editing stuff like that in now. Thanks again!