Heroes of Might and Magic III on GOG
With a vast range of factions, character classes, build options, scenarios and troops, this classic strategy game will keep everyone occupied for hours and hours. The story is also quite engaging in places, especially when you switch between factions. I’ve suggested HOMM III but there is a whole series of these games, including the more recent HOMM VI, if III is too retro.
Genre: Turn based strategy.
Difficulty: There are a variety of difficulty settings available. Start easier.
Age-related suggestions: There’s lots of reading involved, but this should be suitable for any age, really, especially if you play together.
Consider consulting detailed reviews before purchase.