Can I use my chargers from my 6s phone on my new iPhone 12?

Yes you can; however, it will charge extremely slow. 😉

Yes, although they may not charge that fast since the new iPhone 12 has a much bigger battery than that 6s.

You can use both cables interchangeably with both iPhones. For the cable that came with your new iPhone, you’ll want an Apple 20W USB-C power adapter.