The first, Elven Legacy - Ranger, hits October 20, packing 16 new campaign missions and two new heroes. The second, Siege follows November 17, packing 20 missions (19 campaign, 1 bonus) along with two "different" armies and three new heroes. nope
Then on December 1, Magic concludes the trilogy with 16 new missions (15 campaign, 1 bonus), "the return of some older heroes" and "additional tactical possibilities."
Each expansion will be released as a $9.99 digital download--it was not specified if the releases will require a copy of the original Elven Legacy or if they'll be stand-alone.