We are traveling from Detroit Michigan (USA) (DTW) to Auckland New Zealand (AKL).

You don’t need to check in again for your connecting flight at PEK to Guangzhou. Just collect your luggage and follow the instructions to the transfer desk and deal with related procedures.
As for the other two international transfers, you should claim your luggage when landed and go through the customs again. Then, handle the transit procedures and check in to get onboard.

The time should be enough for your first two transfers. For the last domestic to international transfer, the 1hr 45 min layover may be a little bit tight. You are suggested to complete transfer procedures as soon as possible. Or just change the flight schedule if possible.