If I'm reading this right, you do get a signal in bedroom 2 and the hallway (I think it is a hallway on the diagram?) from the current router location, and are trying to get a signal in bedroom 1? It also sounds like you have a long ethernet cable and can physically move the router, at least for experimentation.
Tried that. Tried to move it into bedroom 1 (see yellow circle in diagram), but No difference.
I'd would try temporarily sticking the router either in the hallway or bedroom 2. That should give you a signal in bedroom 1 (unless you have a faraday cage in the walls) but worth confirming. You will need to try somewhere near a powerpoint.
From memory, i only have power point between Master Bedroom & Bedroom 1, Will check again as i moved into this property this week.
If that works, I'd suggest the Google Wifi option from Orcon (or equivalent mesh solution if you're happy to buy - variants do pop up on GZ) with the base unit permanently by the ONT and a slave/child unit in the hallway or bedroom 2. The slave/child unit will sort of act like a wifi repeater, without all the downsides of actual wifi repeaters.
IF, i choose mesh, then will have to place these child units either in Bedroom 1 because placing the router in Bedroom 2 didnt gave me any benefit.