No, each network is separate, you can only see data from one bus at a time. If I remember correctly, some data are not exclusive to a bus (the engine RPM is on the confort bus because it has to be displayed on the dashboard, but it should also be available on the body or inter-systems bus).
You can connect your Arduino to the body bus directly on the “BSI” (basically the car’s computer, with all the fuses on it). See these pictures:
This connector is normally used when you have a trailer hitch, most probably to repeat the car’s lights on the trailer. The red wire is CAN LOW, the brown wire is CAN HIGH. It’s the same speed as the confort bus (125kbps).
I don’t remember where you can get the inter-systems bus. If I remember correctly, it’s available on the OBD-2 port. Be careful, the speed is different for this one: 500kbps. I once chose the wrong speed for the confort bus and everything blinked on the dashboard, I don’t even want to know what happens if you pick the wrong speed on the inter-systems bus 😅