Multi-stream recording

I'm very new to video production and trying to put together a basic video studio at our school. We've got everything pretty well setup but I'm having trouble finding appropriate software for multi-stream recording from our Decklink 8K. Currently we have the TV Studio 4K switcher's Program output and the corresponding SDI outputs for both cameras running to the card. I'd like to have an in sync recording of all 3 video feeds but it seems that the included Media Express software can't really do multi-stream recording without an awkward workaround. I know there are a couple of expensive live streaming programs that are capable of that but at those prices I'd probably just record internally on the individual cameras. Are there any good, affordable options out there?

Possibly useful:

Then again, I got vMix so I'm definitely using it.