@gerlandog, firstly lets look at why your having issues. But remember that Wifi is not an exact science, and normally I would perform a Wifi Audit before making a decision - but that’s a little hard in this case.
TP-Link, D-Link, Netcomm, Linksys, and even Netgear are all domestic Wifi equipment. Designed for the home or office. While these devices do perform well, they have some big limitations due to their environment.
All these devices (to be compatible) run on 2.4Ghz wifi band, and are relatively low powered. Mobile phones, laptops, tablets all run on 2.4Ghz wifi (yes some do run on 5Ghz), bluetooth runs on 2.4Ghz and so does most cordless phones. When you have an area like yours (Plaza) where there are hundreds of people, you start to see that there is a lot of interference happening directly between your Wifi link, and not just a brick wall!. Even people cause issues with Wifi as we absorb/block the signal.
So how do we get around this. Well there is two ways.
1… Use a higher powered commercial grade Wifi Access Point. For this I recommend using an Ubiquiti UnFi LR Access Point. It still runs on 2.4Ghz, but has a range of 185m, whereas most Wifi Access Points are less than 100m (and actually closer to 50m with no interference). What makes this better than others - it’s designed to adapt to its environment and actually uses obstacles to make the signal reach connected devices.
Cost is AU$125
2… Use a Wifi bridge. This is a more powerful solution. For this I would use 2x Ubiquiti NanoStation Loco M5 Access Points. These use 5Ghz wifi band which has very little interference as not much technology uses this band. You point the two access points at each from across the Plaza, as high as you can mount them, and run a network cable from them to your computers, or network switches. These are PoE powered (Power over Ethernet), so you only need to get a network cable to them and power them from the other end at the computers. Two of these can create a 5km 150Mbps link - that equates to 100Mbps ethernet cable connection 5km long 
. At 30m through a brick wall you will need to turn down their power a fair way.
Cost is AU$210
Ubiquiti equipment is built on Carrier Class technology - the same technology used for the mobile phone networks.
Also, you can actually use 2 UniFi Access Points and create a Wifi bridge, but you need to lock them down to a channel in order to achieve this, and that may be hard as there might be many wifi access points in your area and finding a free channel may be hard. I would suggest leaving the channel on auto and let the Access Points find a free channel themselves.
Ubiquiti UniFi LR
Ubiquiti NanoStation M Series
I know this was a little long, but to understand the solution, you need to understand why this is happening and then how the options help overcome these problems.