Jemma is Dan's wife who often appears in his videos. She also has her own channel although it isn't as famous as Dan's. A friend of their's, Leah, is also a YouTuber. Link below. She appeared in the video HAMSTERS! as a person to race Dan in The Great Hamster Race.
In The Sorcerer's Stone, Harry walks with his white owl, Hedwig, through a snowy cloister courtyard located in Durham Cathedral. Harry first learns to fly a broomstick on the green grass of Hogwarts' school grounds, filmed inside the walls of Alnwick Castle, located 30 miles from Newcastle.
It is a part of Islands of Adventure (Hosgsmeade and Hogwarts) and the original Universal Studios Park (London/Kings Cross and Diagon Alley). If you wish to ride Hogwarts Express between the two locations, you need to have a park hopper as you will be boarding in one park and deboarding in another.