If it is showing up twice in the network selection list on the brother. You may have a network issue.
When using the same SSID on multiple access points (routers, bridges, &c). Even on just one device with 5Ghz and 2.4Ghz (basically anything 802.11 ac or later and some 802.11n devices). You need to make sure every setting is exactly the same except radio channels. Radio channels should be left on auto.
SSID (exact same case and any spaces)
Network Key (exact same)
Encryption type (choose precisely the same method on everything, this gets screwed up the most, one can't be WPA2 with AES and another WPA/WPA2 with AES+TKIP)
Also only one router should be using DHCP. If you added more routers as access points. DHCP should be disabled on them and the ethernet plugged into a LAN port. So, that they just act as Access Points. Just note that they won't allow a guest network this way. Unless all routers are the same brand and that brand has special setup options to allow this. Like the defunct Airports did.
If your router is a dual-band model (2.4GHz and 5GHz) it will appear as two separate networks on your printer's network selection list.
It will also appear as two separate networks on your other WiFi devices (laptop etc).
The MK63 system has multiple WIFI source from the satellites. It is not surprising that you see multiple entries. Each of the satellites is an independent WIFI source. Your printer might be confused by that. It shouldn't cause problems. You should be able to pick either copy of your SSID.