Vent/Stub Stack Query

Victorian House

All,

I was wondering if you had any advice on the scheme below. I am looking at redoing the old plumbing in a terraced house. I want to connect two sinks in bedrooms 1 and 2 into the bathroom foul stack and also the bathroom sink into the same.

The bathroom is a half level below the bedrooms so I am a bit worried about venting for the whole system - would a stub stack in the attic over the bathroom do the job? Or will I need to get an external vent into the system somewhere? If I vent outside the bathroom, I have to get the top of the vent over the windows to bedroom 2 which wouldn't look great on the outside. The old set-up has the foul stack at the level of the windows for bedroom 2.