Two routers on one network netgear setup

Thanks for the info.  The Modem is a Arris TM1602A connected to Charter/Spectrum Ulta service and is connecting at around 400 mbps.

What I'm trying to do is split my house so that one level has it's own router and network and the second level has it's own router and network.  Then each person can control their own router, password, and the devices attached to them.

I have a new person moving in and they requested a seprate network with the modem in his area.  They do an online live podcast and say "they use alot of bandwith" and wanted to make sure they can control/reset when needed.  I'm not famillair with exactly how much they would use.  We both stream all of our tv services, four pc's would be in use, plus tablets, Ring, Samsung Smartthings, Amazon cloud cams (4), etc.  

The cable modem would be in his area/floor level and he plans on attaching his router to the modem.  In this case I would run an ethernet cable to my Orbi for my devices...  If we do this I think your are saying I change my Orbi to an access point and let his be the NAT router.  Or, if I knew what I was doing, I'd create a static route on his NAT router and make a subnet for my Orbi?

Hope all of this helps explain what I'm trying to do.  Any additional help/insite would be great.  Thanks.