Except that's the part that is missing...We know Spiderman ISNT an Avenger according to that list and we know. Most Comic book people would say the Avengers "family" could be construed as the core group, which would be Iron Man, Cpt America, Thor, Vision, Hawkeye, Hulk and Ant Man, which were the "Avengers" for over 20 years. Other heroes join in and leave, but does that make them an Avenger?
Without seeing what a "Family" includes, its down to a bunch of comic book guys trying to define at what point being part of the Avengers is being an "Avenger" for the legal term. you could extend this down to the level of is Deadpool an Avenger, because he has been on their team. Are Squirrel Girl and the rest of the Great Lakes Avengers in the family, too, because they were a joke version of the Avengers?
This is the problem that the Disney Lawyers must be arguing with on a daily basis...Unless the character is specifically named (which we don't know that part of the contract), we don't really know what the rights are.