RBR750 Updated Firmware but Satellites didn't update and now don't connect

you can manual update them. log into them using their ip address and do a manual update. 

https://kb.netgear.com/000037217/How-do-I-check-and-manually-upgrade-the-firmware-on-my-Orbi-satellite

if they won't connect back to the router, hardwire into the satellite with a pc/laptop, it should have a default ip address of 192.168.1.250 that you can access it with to update them manually.