You can mix and match SDR mfg's, they don't have to be the same make and model. You just have to build a definition for each one that you add. I got four SDR's running on a laptop that also has a remote TX/RX IC-7100 connected. The limiting factor is how may USB ports/hubs your computer has and bandwidth required for the SDR's. I have an external, powered 4 port USB hub since the laptop only has three physical USB ports. Older USB ports may not be able to handle running two or more SDR's at 6MHz bandwidth, so plug one on one side of the laptop, and the other on the USB port on the other side. Since the two ports on one side share an internal hub within the computer and the remaining port on opposite side has it's own hub. OTW you may get stuttering if operating on max bandwidth and via the same internal hub.
Note, Mine are all run remotely via the SDRC Server and I have set max bandwidth to 1MHz on the server that has a RSP1A on it. All my other SDR's have 192kHz or 912kHz maximum bandwidth capabilities. The SDR-iq and AirSpy HF Discovery respectfully.
I prefer the Airspy Discovery units due to less fiddling with all the gains/attenuators to get proper a display vs the Airspy HF Discovery. Also I don't have to worry about loading the proper drivers from another website to get them to work. The Airspy's units are "Plug N Play" unlike RSPA units where it's "Plug N Prey".
Plus the RSP1A units are plagued with AM BC birdies all the way up to 75 meters and beyond like the RSP1A units I have had. Thankfully I've only got one of those left, and when it dies, I can remove the AM BC filter from the server which hampers those users operating on low end of 160M to VLF.
YMMV
73 Kriss KA1GJU