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.
i7 8700, 16GB, RTX 2080 TI, Rift CV1 | i5 4690K, 16GB, GTX 1660 TI, Rift CV1 | Quest | Quest 2
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).
i7 5820K @ 4.25GHz | EVGA GTX 1080 SC | Gigabyte GA-X99-UD4 | Corsair DDR4 3000 32GB | Corsair HX 750W
SSDs: Intel 660p M.2 2TB, 3x Samsung Evo 1TB | Startech PCIe 4x USB 3.0 | Startech PCIe 2x USB C 3.1 gen2