Well thats the problem, your local areas seems to have some congestion of WiFi, especially on 2.4Ghz, getting to another router, AC even, may not resolve this. AC mode only works on 5Ghz, not 2.4Ghz. You'd still have to upgrade to 5Ghz on those devices to use AC mode.
Maybe someone can review your router settings with you using Link>
teamviewer if your interested. Its safe and secure.