Currently this is correct and the only way to do this.
I have a Quest and a Quest 2. I have the multiuser and app sharing on my Quest 2. I have my main account, lets call it account A as the main account on both headsets.
On my Quest 2, I have a secondary account (account B) signed on as well. To play with my son, I have to sign into the secondary account on my Quest 2 and I have to play on my Quest.
It is a strange setup and I'm sure it will change, but as far as I know, this is the only way to play multiplayer if you own 2 headsets and only want to purchase the game once.