Is there no way you can run cables around the house to where the APs need to be?
I find Homeplugs in my home, even the £100 ones, have a throughput which varies wildly between 90Mbps and 5Mbps, they drop out & anything such as Apple TV or screen mirroring is laggy when going via the homeplug.
If you are going to spend money on this, I would say do it right and get ethernet ran.
E.g. you may not be able to get a wire to the Annex, but somewhere close enough to the annex may work fine. That's just one example.
I would try every possible way imaginable to get the APs hard wired into one another, longer term it will serve you justice.
EDIT: also make sure every AP is dual band. Ideally wireless AC.
Edited by ukhardy07 (Wed 17-Aug-16 12:06:11)