Orbi router in bridge mode over ethernet?

Yes, you could connect a 2nd RBR50 in access point mode at the end of an Ethernet cable in the 2nd house.  I would strongly suggest from the 1st Orbi Router.  It would have a separate wireless network from the other Orbi system, but that should be fine, being in a separate house and all.  And if you need to add a satellite for that separate house, just add it as normal to the router/ap.