In order to play in a household with two headsets, here is what you will need to do. On the headset that is doing app sharing, log in as a secondary account. On the other headset log in as the main account. It is a little counter intuitive, but the only way to have two people play on the same game is for the main account to be logged in on the headset that doesn't have sharing enabled. Having said that, there are still a lot of games that are not available through app sharing. I don't have Fishing VR, so I can't tell you if it is allowing it yet or not. But the set-up I described should work for two headsets. I can play my Quest 1 on the same main account as my Quest 2, but my Quest 2 has to be on the secondary account for it to work.
Eventually two secondary accounts should be able to play together, but for now you can only turn multi-user for one headset per primary account, so there can only be one active secondary at a time (who can play with another user on the primary account).
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