The short answer: Don't worry, as long as you have the private keys for your BTC address, you're fine. You'll be able to import them into forkcoins wallets to claim forkcoins. Both BCH and BTG have 2way replay protection, so "splitting" isn't an issue.
Long answer: There are not likely to be any issues regarding "replay"... As both BCH and now BTG have implemented full 2-way replay protection (
https://bitcoingold.org/replay-protection-development/)
This means you do not need to "split" coins... You just need to make sure you have all the private keys for your preFork BTC addresses.
Then you simply import the private keys into the BCH (and/or BTG) wallet of your choice and you'll be able to get all the BCH (and/or BTG) that are associated with those keys.
The only reason people suggest moving your BTC (after the fork and prior to claiming the fork coins) is for security purposes. It means if your private keys get compromised during export/import due to hidden malware on your computer or a "bad" forkcoin wallet that steals your keys etc, only your fork coin is at risk as your BTC will already have been moved.
As for the coins you had on exchanges, well you're at the mercy of the exchange as to whether or not they're going to issue you the forkcoins for your BTC held there. You don't have the private keys, so technically, you didn't have any BTC either
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