Adding a Router between ONT and Telus Router

[wireless]

Hello,

I live in basement and the guy who lives up have 1000mbps telus. He's happy to share internet but doesn't want me to be on his WiFi and I can't add a second router up there as the range doesn't reaches basement and there is no option to wire, so I'm thinking to add my router first after the NOKIA ONT and use LAN port on my router to give his router access.

I'm just wondering will it break anything for him? Like cameras or optiktv or something will stop working? Will his speeds be affected even if I'm not using it? or he can still get 1000mbps on LAN?

Thanks


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