I do know from utilizing bip39 to construct wallets, that every receiving deal with and corresponding public deal with does have a base58 non-public key behind it. And if I do know this non-public key, I can sweep it separate and aside from my HW pockets, and I can transfer any funds saved there. I’ve performed it.
Now my query: In say a 2 of three multi-sig setup, do such non-public keys (base 58 and even Hexadecimal) exist beneath the hood. And if I possessed these, may they be mixed collectively someway to signal a transaction outdoors of the traditional bip39 pockets construction?