Given an id of any facebook group, using FQL I can fetch all the members of that group, if I am a member of that group. I can also see who of my friends is in the same group as me, that is also not a problem. Now, I need to see of all of the group members, who of them is friends, I mean, if there are 2 group members in the same group as me, but they are not my friends, is there any way to see if those 2 are friends?
Without each of those friends giving you access to view who their friends are, it's impossible.  If Facebook allowed this to happen without a friend granting you that access, then I'm going go scream from the hills about a HUGE security hole.
How to see mutual friendships in a facebook group?