If the building is already connected, there may be a Hyperoptic faceplate already installed, in which case you need to do nothing, just plug in an ethernet cable and connect it to the router. If your brother has the address, phone Hyperoptic, I'm sure they'll have the details of what's been installed.
If it hasn't been installed, then yes, it will probably involve a small hole being drilled near the front door, and a cable fed through it and cable tied to the wall, and a faceplate installed nearby a power socket. If this is needed, then you should get permission from the landlord. but you'd hope they would see the benefit. When they rent it out next year, it'll help attract renters. Just ensure the landlords permission is in writing and the agency get a copy if there is one.
The BT faceplate is nothing to do with Hyperoptic, and will be left untouched. Allowing for a BT service if needed.