The rooms can be grouped. Or you can add 2 (but not just 1) One’s as surrounds bonded to the soundbar. 

Note, when ‘grouped’ as two separate rooms, the One will be slightly delayed from the Arc, by 75ms. If set up as a pair of surrounds, you won’t get the center channel (where speech occurs) out of them. 

Sonos currently has no great solution for the hard of hearing where TV input is concerned.