Sheikh, here is a thread with a connection diagram. https://discuss.bluerobotics.com/t/bluerov-interconnect-diagram/
You have thrusters with the ESCs built-in, these ESCs are controlled via I2C communication protocol rather than pwm.
the 4 wires are the I2C lines, look for the documentation on the bluesc product page in the bluerobotics store.
Yes, you can connect all of the thrusters’ power wires in parallel and run on a single battery.
-Jacob