Is that an assumption or you confirmed with your neighbor that he is actively blocking your SSIDs? Pretty sure that isn't 'legal' but since it is France, I'm not certain.
If its being blocked it would be an immediate thing, like you would connect and within a second or two, disconnected, and repeating over and over.
If your connected for 15 minutes or a few hours and then it disconnects, it most likely isn't that.
For sure would want to talk to them to confirm you guys can work together, and I would make your SSID's 5GHz only if you can.