I'm really sorry Metro but it's still not making a whole lot of sense to me. Maybe the fact I'm not a native English speaker is rearing it's ugly head.
I don't see how Lily's explanation and Pam's explanation can both be accurate. When considering the first-time Ambrosia requirements, Best Friends must either be unique or not. Can't really be both.
Maybe an example will lift this fog from my brain:
Say Sim G1 (Generation 1) has 2 other people living in the house (a spouse and a housemate). Sim G1 is Best Friends with all of these people. Then Sim G2 is born, and while growing up becomes Best Friends with all the people living in the house. Can Sim G1 then have the spouse and the housemate for their Best Friend Ambrosia Requirement?
If the Best Friends have to be unique then I'm inclined to think no, because there's overlap with Sim G2. Similarly, Sim G2 won't be able to claim them either because there's overlap with Sim G1. So that'd exclude most significant family relationships from being able to be claimed, since it's fairly hard (or cruel?) to not have heir and spouse become Best Friends.
Am I finally starting to understand this or do I still have it completely wrong?
On a related, but slightly different, note: Can the Gen 1 Sim put the Gen 2 Sim on the BF Req. List (since obviously Gen 2 Sim can't be Best Friends with him/her self), or is this considered sneaky and not allowed