I have 3 separate GPS antennas. One is an older Raymarine antenna that supports a Raymarine GPS head and the Raymarine chartplotter. I also use Coastal Explorer on a laptop that can select which of the 3 GPS sources I want it to use with automatic switching to another unit should the first priority go down. The other GPS sources are a GPS puck and an antenna that signals my Vesper XB8000 AIS. Currently on CE my priority is the Vesper unit. There are small difference occasionally between the older Raymarine and the new Vesper, but not enough that it worries me.
As backup, I also run 2 separate IPads with Navionics and each IPad has it's own built in GPS, so in essence, I have 5 GPS antennas (signal sources). Now, let's make sure the entire system does not go down