Wifi coverage in house sucks

I live in the Alcatraz of the Wifi signal. Double story house with the floors seperated by a concrete slab, impenetrable by any wifi signal. We have been chugging along with ADSL with the router in bedroom 1 with a little TP-Link extender in the passage close to Bedroom 4 and the study. The router signal was only good to Bedroom 3. Downstairs was never really had coverage. At a certain angle you could get the little extender signal down the stairs double volume but that little jobbie is not great. Works ok but it is slow.

Now we got fibre and they installed it to the study. It was the easiest route. Now the question, what can I do to get the wifi signal through the house? What will you do? Obviously there is a cost element to it but willing to try do it properly. Also want to run LAN cables to Bedroom 1 (DSTV/MEDIA box when I convince the wife DSTV is crap) and Bedroom 4 (Sons room for his laptop). Can I run a 20m+ LAN cable from a router (D-Link something-or-the-other)? Will get the proper model no when I get home.

Any suggestions will be very welcome. No budget in mind yet, will consider all options, bearing in mind it is a residential home. Your help will be greatly appreciated.