Regarding the Android, the latest version is 11 so I suggest updating that. Also, the network analyzer app from Netgear provides a lot of useful insights, like whether there's any interference on the network and suggests which channel to use. On your own you can try troubleshooting your phones with that.
Typically for troubleshooting wifi devices, our engineers suggest first switching networks to see if there's a difference (I see you've tried that), and then to also power cycle the modem and the wifi device.
To power cycle the modem, the power cable should be disconnected from its power brick (not from the back of the modem) for at least 20 seconds before replugging. A device can just be powered down for 20 seconds before turning it back on.
First lets check on the directly connected laptop with wifi on the modem disabled so we're sure it's isolated and gather this info:
Which URLs are you testing (I suggest whichever one's you frequetly struggle with)
How long does each URL take to load?
Have you ever been able to successfully visit that URL?
When did you first notice having difficulty visiting that URL?
Have there been any changes to your system prior to your concerns?
Does disabling Web Acceleration make a difference? (Enter 192.168.0.1 in your browser then follow the steps here to find where to toggle Web Acceleration: http://hninfo.us/WAS)
Does this happen in different browsers?
Does this happen even after clearing your browser cache? (How-to here: refreshyourcache.com)
What time did you test these URLs?
Is there any difference in page load times if done at different times of day/night? I suggest checking in the morning, midday, and evening if possible.
I know this is a lot to do, but this should be enough to present to engineering if we can't pinpoint a root cause.
Your cooperation, patience, and understanding are greatly appreciated so that we can address your concerns.
Edit: More troubleshooting steps typically suggested by engineering:
Disable uPnP, any difference in load time??
Change security setting from WPA2 to WPA/WPA2 in wifi settings on the modem
Disable IPv6
-Liz