BTG moves for now quite independent from BCH and BTC.
However, they are all related.
When bitcoin got its upward move, BCH goes down.
Whenever BCH moves up, BTC goes down.
But what about BTG?
What I assume is this:
BCH will be 50% of BTC
BTG will be 25% of BCH
BTG will be 5% of BTC
Remember:
Forks are always priced in.
At the moment of writing is
BTG 345
BCH 1450
BTC 6300
total: 8K, target price of segwit 2X.