Wireless connection dropping

Hey, I'm having a problem with the Wifi in my house and it seems to be related to one Mac in particular.

I'm going to try and include as much information as I can so sorry for the long read.

Ok so this problem has been very persistent, basically the internet in my house keeps dropping on all of my devices. My internet provider is BT (infinity) who I have spoken to numerous times on the phone and gone through many different checks with them over the phone, changed the wireless channel through the gateway etc. the problem still went on so I've had new routers (both BT and open reach) and 2 engineers have been to the house, one of them being the senior engineer. They have worked with the wiring inside the house and checked the line from BT themselves into the exchange and the box outside in the street. Both engineers left certain that the problem had been solved but after they had left, the problem returns.

I've come here because the one significant thing about this problem is that out of all of my devices, one iMac in particular seems to be able to reset the wifi and make it work. If I turn the wifi off then straight back on (on this mac) all the devices in the house start picking up the internet signal again.

Altogether, connected to the internet I have, 2 imacs, an iPhone 5, and iPad air, 2 sky boxes, a MacBook Pro, and 2 smart tvs but only that one Mac can reset the internet. Also resetting the modem can bring back the connection but as you can probably imagine having to constantly do this, especially whilst in the middle of a task is overly frustrating especially over a long period of time.

I've looked online and followed some instructions on the tcp/ip and DNS settings but still nothing.

Does anyone have any ideas on what I could do or why this could be happening.

Thanks