Can I copy an iPhone to a second iPhone of mine with different SIM cards and use both?
Yes, surely you can do that.
In general, there's nothing hindering you from having multiple phones logged into the same Apple-ID - but with different SIM-cards and phone numbers. I.e. you do not need to copy an existing phone in order to achieve this - you can also just setup a new phone as a "blank" device and login to your Apple-ID.