The exterior and some of the interior sets of Auradon Prep is the same ones used for Xavier's School in X2: X-Men United (2003), the Luthor mansion in Smallville (2001) and the Queen mansion in Arrow (2012).
In the Tourney game, Cameron Boyce's character, Carlos, plays the game as number 101. This a reference to his mother, Cruela De Vil, from One Hundred and One Dalmatians (1961).
The reason Ben decided to ask the villains' children to come to Auradon was because he had a vision of a girl like Mal on the Isle of the Lost, but it's never explained in the film itself.
Mal isn't her full name. Maleficent, her mother, won't give Mal her full name until she proves she is evil enough.