"repair" does not mean what you think it means. quynhphan, you need to redo the pairing procedure.

What? English please!

Three phase wiring is very common in continental europe, so no problem there. All power wiring being unshielded, the high frequency data transmissions will crosstalk into the other phases well enough...

Yes of course, the LAN jacks on powerline devices are as universal as those directly on the router; in the outer building you'll need a WLAN accesspoint/repeater device and set it to access point...

Using consumer PLCs, this looks like the mother of all bad ideas to me. Using slightly better PLCs that let you pick non-overlapping frequency ranges (very much as you would on WLAN), it might work...

Unless your network of access points actively force the client device to the closest or best one, the client devices will switch over only if and when they feel like it. Some rescan for a better AP...