If the ATEM doesn't give you those cameras already, then nothing on the PC side will get them for you. If you want to have them separately in OBS, you have to bring them into the PC separately first.
I suppose it's *possible* for a multiple-input USB capture card to exist, but I've never seen one. The ATEM is not one either: it's a single-input capture that is fed from a hardware compositor, all in the same box.
You might look at these, instead of the ATEM:
Acasis PCIe capture card supports multiple HD resolutions (such as 4K60Hz), bringing crystal-clear visual effects to the audience. It also supports quad HDMI or SDI simultaneous input, allowing you to flexibly adjust between different camera angles or input devices. Solve your professional video...
www.acasis.com
PCIE CAPTURE CARD AC-4HDMI (Quad HDMI-1080P60).zip AC-4SDI (Quad SDI-1080P60).zip AC-4HDMI PLUS (Quad HDMI-1080P60).zip AC-4SDI PLUS (Quad SDI-1080P60).zip AC-VS2583 (2 HDMI-4K60).zip AC-VS2584 (1HDMI+1SDI-1080P60).zip AC-VS007 (Dual HDMI-1080P60).zip AC-VS014 (2HDMI+2SDI-1080P60).zip AC-VS049...
www.acasis.com
Then the ATEM goes away completely, and you do everything in OBS.