@Toastkid6 

There are very few options to pass Ethernet through the thick wall, and this is what you will need. 

1. Ethernet cable is the best option, but obviously you don't have that or you won't be posting here;

2. If you have coaxial (TV) cable between office and rest of the house, it would be possible to use that. Let me know and I'll share details.

Other than that, powerline is really the only other choice. 

P9s will switch to WiFi when there are issues with powerline link, such as too much electrical noise from other devices connected to the same circuit breaker. Google for hints and tips on how to use powerline adapters and what impacts powerline adapters performance, what you'll find should be applicable to P9 powerline connectivity.