If I got a game pass ultimate subscription would I be able to play space marine 2 through...

as the game is not part of game pass you would need to purchase the game digitally

1) No.

2) If you purchased the games, you won't lose them. If you downloaded them for free through EA Play, you would no longer be able to play them with an EA Play or Game Pass Ultimate subscription.

If you were to buy Game Pass Ultimate, that would be true and you would be able to play the game and play online. However, for people who only buy Game Pass Core, the game is not available through that subscription and they would need to buy the game. If the game is eventually removed from Game Pass, you wouldn't be able to play it without buying the game either.

Just to make extra sure:

Are you having Game Pass Ultimate, or just Game Pass (without Ultimate)?

If you say your sister can't play online Multiplayer, then you (or she) would need a separate Gold Membership or an upgrade to Game Pass Ultimate.

Game Pass allows you to play the games available in the Game Pass subscription. But to be able to play online Multiplayer, a Gold subscription or Game Pass Ultimate subscription (which contains Xbox Live Gold) would be necessary.

My girlfriend had recently got game pass ultimate and we said we would gameshare it. Her home xbox is my xbox and my accounts home xbox is on her console. The subscription is only showing up on her xbox and is not transferring to mine also how do i fix this?

Gamesharing through the "Home" feature does not share the Ultimate subscription. "Home" console lets you play any of her purchased and downloaded games even if they are from Game Pass. Your account will not show as having Ultimate, and your account will not be able to utilize Game Pass PC or cloud gaming. Those features are only for the account that actually purchased Game Pass Ultimate.