No, ISP sees the IMEI (International Mobile Equipment Identity) and IMSI (International Mobile Subscriber Identity) of your mobile device or modem. The MAC address is not transmitted over the cellular network.
The ISP can't, but the upper network can, of course.
Depends on if the cable is connected to another router (then same like with repeater) or connected directly to the Internet (like with fiber sometimes) - if that's the case, then yes.
You can always randomize / change your MAC and/or IMEI.
Please be aware that this might violate laws and or contracts.
I cannot control that router. There is only password and name setup settings. That’s all. It not even physically located in my apartment (it is outside, right behind the wall, locked in box)