Looking for some guidance around how I can extend range of our single VDSL router (HG659) at home. Apologies if this has been answered elsewhere, please provide any links which maybe helpful if I'm regurgitating something.

We live in a multi storey flat, with our VDSL connection coming into the house in the bottom storey, in the corner. This isn't ideal, and is impractical for us to try move this connection to a more central location. 

We have tried using Powerline adaptors (Wifi adaptor - DLink DHP W-310AV) to try extend the range in the other corners of the house, but it seems the connection cuts out at various times and isnt stable enough - we have triple phase wiring in the house that differs between upstairs and downstairs, i'm not sure if this causes issues with the powerline adaptors? Funnily enough, the Dlink wired Ethernet adapter (DHP 309 AV) seems to work fine when linked upstairs and downstairs to where the router is but this only has one Ethernet output.

The question - we have a whole bunch of old ADSL routers (HG556a, TG589vn v2) - can we use any of these along with the Powerline adapters to extend the wifi signal throughout the house? Being pretty cash strapped, we'd rather have a play around and see if we can jimmy out a solution using existing devices. Or alternatively, open to any reasonably cheap options which will solve our issue.

Appreciate in advance.