In sha256 or even sha128 you will never have the same output.
You definitely will.
Taking SHA256 as an example - the output is always 256 bits, so there are 2
256 possible outputs. However, the input can be up to 2
64 - 1 bits in length, which works out to any data up to 2 million terabytes in size. Therefore, there are exponentially more possible inputs than possible outputs, so collisions are guaranteed.
And as I understand it, you always have access to all sub-accounts created in the main wallet, no matter what the first generated address is. I mean when I log into Metamask with the seeds I have the same address as Exodus or the recently tiled Atomic Wallet, that's what I mean by main wallet.
The same seed phrase will always generate the same addresses at the same derivation path, regardless of what wallet you use (provided all the wallets are following the BIP39 standard and not doing something completely unique).
What do you think it is possible to get access to the same coins with different seeds? Or did I record there stupid stuff?
Technically speaking, given the number of possible derivation paths, every seed phrase in existence is almost certainly capable of generating every possible address. But in practice, there will never be an address collision before the death of the sun.