@Nicholas446 As they are already on the reservation, it likely won't be an issue, but notifying the host of the change of plan is certainly the proper thing to do. It is actually still considered a third party reservation, as the person who booked won't be staying. The host might ask that it gets rebooked under the account of one of those who will be staying, and in that case, you'll need Airbnb to help facilitate that.
As the booker, though, you will be held responsible for the behavior of the other guests (and the review will appear on your profile), so make sure that they have read thoroughly through the listing description, are aware of and willing to respect the house rules, and communicate arrival time and such with the host.