You can only set one Switch as primary account.
you can play with your own account in your own switch, while your friend plays in his Switch that is set as your account’s primary. Previously both can play the same game at the same time (I did a while ago to play MH rise with my friend, using one game and one NSO subscription). Seems this is no longer possible after the new update
Enable quick share to receive from everyone (if using different google account) in receiver side, this should be there in quick setting from swipe down (if not there, maybe it’s hidden, try to find it in edit setting). And then on sender when sharing, just use quick share. It will then show nearest devices.
Afaik, it will use wifi to transfer the file, so it’s much faster than simple Bluetooth
Yes, we did play online on the same party. In contrast, we can’t play local network party together so need to be Online