I2C is a bus system and allows you to connect multiple sensors to the same pins. The master system (the Pi) lets the sensors know who should respond by placing that sensor's address on the bus.
In your case you can connect all the sensors I2C SDA pins to the Pi's SDA pin and all the sensors I2C SCL pins to the Pi's SCL pin.
Note you can also connect all the ...
Chapter 3 of the available documentation states that all of the hardware-based I2C buses on the BCM2711 (RPi 4) operate under the control of the Broadcom Serial Controller, or BSC. The RPi hardware and firmware are closed-source, but relying on the documentation, a reasonable assumption is: "No - none of the hardware-based I2C channels are faster than ...
All the 8 hardware I2C buses on the Pi 4 are identical.
The Broadcom Serial Control (BSC) controller is a master, fast-mode
(400Kb/s) BSC controller. The Broadcom Serial Control bus is a
proprietary bus compliant with the Philips® I2C bus/interface version
2.1 January 2000.
AFAIK the MXL7704 device on the Pi4 is managed by the Video Core and not accessible to the CPU.
It doesn't "measure" the voltage it uses an in-chip comparator.
The MXL7704 data sheet is readily available.
INT_SCL and INT_SDA are not shown as connected to the expansion header (as far as I can see).
Perhaps they are connected to one of the other I2C buses on the Pi4.
I suppose you could try writing drivers for those other buses.