Congrats Grace! It's definitely your BRP! I'm sure you can reschedule it since no one's at home. And your IDs would be fine. If they have photos, the better. Also, if you can supply a letter that contains your name and address as proof, that's fine too. They just want to know it's really you on delivery name.

About your documents, Royal Mail needs a signature too. If no one would be at home to claim it, they would leave a note that they have a package for you and you should claim it at the post office they indicate.

Anyway, congrats again!!!