Pembroke's wolf is strange, white fur tipped with red. He is unaffected by the incense and Alpha weapon. It was said before Cassandra is actually a witch. It sounds like Pembroke himself is cursed.
I'm thinking he might be slightly older than George. Cavendish was a senior lieutenant to George when he arrived on the Victory in 1793. This would put him in his early 20's now.
I'm sorry, but even so Rory is bitchy and selfish. This isn't all about him. The lives of all the people of both kingdoms depend on their success and he insults Garran. This will be a lesson for Rory as well.