can any bitcoin wallet hold - bitcoin gold, bitcoin diamond etc - im looking at buying btcx but it shows as bread as the only ios wallet
No, bitcoin, is different from the other forks.
Most forks (btc gold, btc diamond, and btc xx) are shitty altcoins, you should understand that, so whatever you do, do not buy them because they are just created for fun purposes, they are not technical.
And you can not store them all on the same wallet, maybe you can buy a trezor or a ledger and you can store them all in the same device (not the same wallet)
But dont buy them, they are useless.