How smart is a buddy-backup network regarding slow connections and multiple backup targets?

[wild-dog]

So here is my situation.

I have 2 NAS-es, 1 In my home (NAS A), 1 in my parents home (NAS B).
NAS A is on a gigabit fiber conenction.
NAS B is on a 80/80 mbit up/down connection.
A and B perform buddy backups to eachother.

I'm adding a larger storage server C to also hold backups for both.
C is also behind a gigabit connection.

Does the initial, 8+TB backup of B to C also have to go through the slow 80/80 connection?
Or can it use the existing backup on A which is behind a gigabit connection, so it does to not take 14+ days to synchronise the initial backup?

And broader, once setup, does B have to do a slow upload of the differential backups to both A and C every time, or does it only have to do an upload to one of them, so they can then internally replicate?

Edited 7 hours ago by wild-dog

[PsychoWards]

Hey, Buddy Backup is always peer2peer, so each server is backing up to each server directly, you cannot pass through another server or get the data from another server. 

If possible, I highly recommend to do the initial backup from B to C locally and only then move C to it's final location.