Existing game pass subscription and buying series x with all access

It'll be redeemed through the console itself, it's not a physical code, but you don't have to redeem it as soon as you get the console.

Thank you for you assistance, I wasnt aware that the game pass subscription that's part of the all access was a redeemable code.

You would have to wait until you have 12 months of Ultimate left before you redeem the 24 months of Ultimate since you can only stack 36 months at a time.

Since the games are made for a Series S/X, then yeah, if you had a Series S/X console and could install the games, then everyone could play them. Sharing the subscription (as it currently works) only allows other profiles to access certain benefits such as accessing any games you download from the Game Pass subscription and the ability to play online. Other benefits are only available to the account that purchases the subscription.

If you buy game pass Ultimate, it will convert your existing subscriptions to the Ultimate sub. Once it is all done, if you check your subscriptions at accounts.microsoft.com it will show the new Ultimate pass, and the old Subscriptions as Cancelled.