Do I need an ID card to travel with a group and stay in a hotel? Do I need to have the same ID card as when I signed up for the tour?

At present, all hotels in China need ID card registration. Generally speaking, when traveling with a group, a group must provide at least 90% ID card before the hotel can check in. So, if you have an ID card, you'd better take it with you.

"Does the tour group have to be the same as the ID card?" I don't quite understand what you mean. Generally speaking, the ID card (usually ID number) provided at the time of registration is used to purchase travel insurance or air tickets. This must be the ID card of the participant, and it cannot be replaced by someone else's ID card. When there are insurance claims, you must also check them.

As for the ID cards used when checking in, they are generally not checked one by one.