Brother printer keeps dropping from network

Have you thought about setting up an IP address reservation in the router (probably in the extender too)? Reserve an IP address out of the DHCP range, and then use Socket/jetdirect protocol to connect to the printer from computers/devices.

Getting the printer to always stay on the same IP address is a function of setting it up in your router. Once you have that, you can add the printer using the Add Printer dialog - using the IP address you gave it.

Have you tried rebooting the router?

When you reset the wireless settings on the printer, did you restore it to factory defaults first?

You should also check to see if your WiFi network is using the same channel as any neighboring WiFi networks. You can try setting your router to auto set the WiFi so it can automatically choose the best channel, but if it is already set you could try manually setting the channel to see if it solves your problem.

Are all the problem devices connecting through the AP?

I would say simplify the network for testing purposes. Remove the AP and make sure everything connects and communicates properly with just the wireless router. If things are fine, add the AP back into the mix.

You probably should be logging into the router & AP to check their logs, settings & verify the connected devices.

Get a new printer. They're dirt cheap these days. For consumer grade printers, it's sometimes cheaper to buy a new one than it is to replace the ink cartridges when they run out.

Besides checking for other neighboring WiFi networks using the same frequencies and causing interference, you should check each device to see what type of WiFi connection each is using such as g, n, etc. to see if there is any pattern between the working & non-working ones.

Jetdirect-socket is a standard network printing protocol (a way that computers talk to printers).

In System Prefs, go to Printers and Scanners, then click on the "+" to add a new printer, then click on IP to see standard network protocols.

Do your computers have Ethernet?

Just one example, there are many like this...

• Kit includes two adapters that use existing electrical wiring in your home to create a network connection

https://www.amazon.com/NETGEAR-XAVB101-Powerline-Ethernet-Adapter/dp/B001AGM2VI

It uses existing electrical wiring, (A/C plug-in sockets), in your home to connect computers or routers or other network things... it's like running Ethernet cables through your house but without having to do any wiring.

https://www.amazon.com/dp/B008F537KC/ref=sspa_dk_detail_0?

Whew, not much left to do, but check USB mA in System Profiler on the Macs... Wifi Uses USB mAs...