Sally Jackson is James Potter's sister. Sally is friends with Severus. Sally doesn't want anything to do with the war and hides besides some type of magic or wards, but Dumbledore finds out how to go through them only to get Percy on their side.
Sally and Percy want to keep it a secret from Harry that they are family. Percy is the physical education teacher at Hogwarts. Percy takes the curse Katie got from the necklace with skin contact. I think it was set after the Giant War.
The golden trio is suspicious of Percy. And I think that Percy and Severus have an almost brotherly relationship.