TLDR: Try using USB over IP instead of USB2 over USB3.
A quick googling shows that your exact question is not possible.
Any USB 2.0 hub that supports a higher standard than USB 1.1 (12 Mbit/s) will translate between the lower standard and the higher standard using what is called a transaction translator (TT). For example, if a USB 1.1 device is connected to a port on a USB 2.0 hub, then the TT would automatically recognize and translate the USB 1.1 signals to USB 2.0 on the uplink. However, the default design is that all lower-standard devices share the same transaction translator and thus create a bottleneck, a configuration known as the single transaction translator. Consequently, multi transaction translators (Multi-TT) were created, which provide more transaction translators such that bottlenecks are avoided. Note that USB 3.0 hubs do not currently perform transaction translation to super-speed for USB 2.0 devices.
However. On a related note, what IS possible, is to encapulate the USB 2.0 across TCP/IP over Fast/Gigabit Ethernet.. Essentially building a Transaction Translation module.
You could then connect the USB 2.0 devices to a lightweight PC that tunnels the USB over a ethernet connection. I would advice you use Gigabit ethernet, given that you have bandwidth requirements (please don't try to use Wifi). You can therefore run a gigabit ethernet over USB 3.0 on your laptop.
However, on your IP/USB hub side, your options are more limited.
You'd want a "low" cost single board PC with both a gigabit ethernet and a USB 2.0 (or better) controller.
I would suggest you take a look at the Banana Pi, which has a single USB 2.0 controller (2 ports) and a gigabit ethernet controller.
Even so. I'd expect pretty high latency on the link, which would make your Pro Audio Mixer useless. Luckily the HD Cam should work with the high latency (given it already is pretty high latency already).
All in all, I'd expect this project to run into ~100USD.
My recommendation now would be to use the Orange Pi Zero Plus. It is a small SBC with GbE and a USB2.0 connector, and not much else.