It will work, but the main router in the network will be the first WS5800 and the second satellite, it connects via WiFi to the first one on the 5GHz band dedicated for this purpose, because the WS5800 is AC2200 and MESH on 3 2x5GHz and 2.4GHz bands. B818 only plays the role of an LTE modem in the bridge, not a router.
Same for me, only instead of B818 I use MC7010, it is an external router, integrated with the antenna, without WiFi and set as a bridge, it provides access to 5G / LTE, and instead of WS5800 I have these two COVR2200 and they work just like your WS5800.
The second solution is a different league, because the source of the Internet is the Netgear LBR20 router, it is the equivalent of B818, but it already has the MESH function, so it is also the main router in the network, it also has AC2200 and a dedicated 5GHz band for communication via WIFI with additional satellites, I use it for it as satellites, two Netgear LBS20 are connected, they act as additional APs.
I have a Cybertech antenna connected to the LBR20. The basis for you is an LTE router and an external antenna for it.
I hope you now understand how it is supposed to work.
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