Question about Netgear Orbi RBK50 set

You have to set the router to bridge mode. This should actually work with modern routers, the Orbi system is then more or less the continuation of the router. The nice thing about this is that the coverage also works in complicated buildings and Powerline etc. can usually be dispensed with. The entrance router should be in a reasonably central location (in my case it's on the lowest floor and the WLAN network is good enough even on the third floor).