Normal practice would take the cable in through the front and run internally, drilling internal walls as needed. Running across other people's property or right round the entire terrace involves cost and complexity that mean they won't happen. And running over the roof or through the loft is unlikely to be viable - needs a "working at height" team, ladder access back and front, safe access to loft space, and probably won't happen.
I could be wrong, but unless they can use the normal route, I doubt you'll be getting VM installed at all. Wait and see what response you get, but I'm guessing that the order will be cancelled unless you agree to internal cable running and the wall mounted box where the technicians want to put it.
Make sure any existing ISP contract remains in place until/if any VM installation actually happens.