Can I use multiple ClonerAlliance Chert 4KC devices on one PC at the same time?

Sure, both bundled software HDML-Cloner Pro Helper and OBS studio can support multiple ClonerAlliance Chert 4KC devices working on one PC at the same time, you just need to add and select devices individually as following:

OBS Studio add multiple video capture devices

OBS Studio select multiple video capture devices 1

You can easily distinguish each device through video preview window.

OBS Studio select multiple video capture devices 2

And you can select an audio device for each video capture device based on the insertion order.