RBK40 and Nighthawk for 2 wireless networks

I know this sounds crazy but I'm wondering if I can use an old Nighthawk router to provide one wireless network for a specific area but connect it to an Orbi for a second network to continue to serve the rest of the house. 

I have a Nighthawk router that was always rock solid but did not deliver wifi to the whole house (old house, lathe and plaster, petrified beams). So I got an Orbi RBK40 (Woot) and 2 sattelites a while back.

I have it in AP mode and use the old Nighthawk for the router function, wired to the Orbi. Now I get great coverage... but like sooooo many people, dropouts. This does not impact anything in our downstairs so TV/Streaming/browsing are all just fine. And the occasional dropout of my VPN for work I canl live with for the sake of the coverage. My wife's VPN always stays rock solid but she is near the Orbi base while I am connected via a sattelite that seems to be the problem. (I have tried every suggested solution to the dropouts except the telnet trick to separate the SSIDs.)

However, I have a gamer in the house and the dropouts kill his online gaming. He's on a collegiate team and dropouts during inter-college competition is pretty bad. He never had any dropouts when it was just the Nighthawk. The only way he can reliably compete (and take video classes over Zoom!) is to run a wire 30 feet from the Orbi base to his room, which is a mess (the wires, not his room). 

I'm wondering if I can put the Nighthawk back into service to broadcast one network with its own SSID just for my gamer, but leave the Orbi wired to the Nighthawk to provide a second network and SSID for the media room and business use. 

Is that possible? What will be the downsides? (I know, make sure the two networks are on widely separated channels...) But will this work at all?