Upvote:4
Would this be a red flag for the immigration officers?
No.
Advance accommodation arrangements are not required by the UK for visa applications. Any accommodation details that you provided at that stage do not have to match the new details.
As long as there is a reasonable arrangement, and you don't make up things at the border; This should not be a problem at all.
If the new bookings that you have are valid bookings, there is no harm in presenting them. If he will be staying at your father's place, there is no harm in mentioning that if asked.