Tranfering game data to a different device from a different Gamecenter account

If a game’s data is tied to an iCloud account but I only log in to another user’s Game Center account, will I still access their game data? My game is sneakysasquatch and I have been playing on my brothers account from apple tv. And now I have my own IMac, I wanted to transfer that game data to my own device. But I have logged in to my own apple Icloud, and I've tried logging in to his Gamecenter account but no save file was showing. Can someone help?