I wanted to ask you guys if it's possible to install nethunter on copperhead os?
No, Copperhead OS is about securing the device in every possible way including limiting all functions which are not in a normal phone.
NetHunter on the other hand is more about extending the capability, which in some cases requires lowering the device security.
So if you need a secure device, don't install NetHunter on it. If you are trying to test the security of other devices or networks use NetHunter.