Movies using the X-Men characters are also licensed to Fox. Although a two of them (Quicksilver & Scarlet Witch) appeared in Avengers: Age of Ultron, Fox placed restrictions on them. Marvel couldn't refer to them as mutants and had to use a different actor for Quicksilver.
Although Marvel will be co-producing the next standalone Spider-Man movie, it will most likley not be available to
DCL since it will still be released theatrically by Columbia Pictures (a unit of Sony). As part of the co-producing agreement, Peter Parker/Spider-Man will be appearing in Captain America: Civil War. Unlike Quicksilver, the same actor will play Spider-Man across both movies.