Three airport extremes. How can I get the best/ fastest wireless experience out of the set up?

I have Verizon Fios with a fairly new Verizon router. I have cat 6 Ethernet going from the Verizon router to a Netgear gigabit switch then cat 6 running 21 Airport extreme on one side of the house, to an airport extreme in the middle of the house, then to an airport extreme on the other side of the house. I have tons of connected devices to the network such as Nest thermostat, 20 or so Hue light bulbs, couple Mac MacBooks, three iPhones, three iPads, couple Windows computers and gaming equipment. How can I get the best signal/ fastest wireless speed. It seems as if one of my routers is handling more devices than the others. Is there a way to set up A roaming network with airport extremes? I wouldn't say I'm a complete novice when it comes to networking, but I'm at the point of my knowledge base where I'm not sure what else I can do. This is the first time I've posted to the Apple community. Please be gentle LOL. Thank you very much in advance.