Agreed.

Pretty much any combination works as long as every character on you group is on an account linked to the account of at least one other character in the group.

A recruits B, C, D and E would also work as everybody is linked to someone.

Now you might have to think in terms of "giftable" levels.

A recruits B and C
D recruits E

means that for each level 60 group levelled, you will be able to gift 60 levels to account A and 30 levels to account D.