Playing the same game at the same time on seperate consoles on family set up

you both need your own accounts.

you will also need Live Gold on one of the accounts unless you have Ultimate Gamepass which includes Live Gold

player 1 (has Gamepass/Rocket League) makes Xbox B their Home Xbox then plays on Xbox A

player 2 plays on Xbox B

player 2 can make Xbox A their Home Xbox so that any games purchased on their account can be played by player 1 on Xbox A

https://support.xbox.com/help/hardware-network/console/my-home-xbox

You can only share games on the console that is linked as a home account, this is not shared across to other consoles that they may log into / use

It can we play the same game at the same time?

Hi,Chris! I'm Luis, a fellow Xbox Gamer . Thanks for reaching us out here.

You just need to use the "home xbox " feature.

Withe the account that owns the game on the other console please:

Press the Xbox button  on your controller to open the guide.

Select Profile & system > Settings > General > Personalization, and then select My home Xbox.

Select Make this my home Xbox.

After that games and subcription bought with that account will be shared with the other console

Yes Chris. But you need two accounts for that.