The 4 rooms, in the following order: office,kid1,kid2,main are located to the left of the hallway. So there are 4 walls between any of the routers and the main bed-room where the signal is low.
If I walk along the hallway, such as in front of the main bedroom, I get maybe a 3 bars signal.
I have to be almost at the office door to get a 5 bars signal from any of the routers.
What I find strange is that I get a 4 to 5 bars signal on many of the AP of my neighbors, apparently, no matter where I locate the notebook in the house.
The AP is at the level of the desk. I'll put it on top of a books tower or some.
It doesn't have any external antenna, tough.
There aren't any mirrors but the 3 rooms all have wall-mounted closets that stand in the way.
I've learned that there are WiFi repeaters, such as "Tp-link Tl-wa901nd" which I can get for about U$S80 here. Would that help? Should I put that say in one of my kid's room?