You can certainly group two rooms at will in the Sonos software. Or, for that matter, ungroup them.
Note that any room grouped with a TV room, and playing an input from the TV, will be slightly delayed, by at least 75 ms. This shouldn’t be a problem when you can’t hear both rooms at the same time, in fact I’ve done this before with my TV room and my kitchen. As long as I didn’t stand in the doorway between the two, it was fine. And since I don’t have the need to stand in the doorway…
However, that same grouping, when streaming music from the internet (not the TV input), will be in sync, 100%.