Is summarizing foreign stories for the purpose of language instruction and reviewing their illustrative drawings considered a sin, thereby rendering the earnings unlawful?

Earning from summarizing stories shares the same ruling as the work itself: if the work is permissible (halal), then the earning is permissible; and vice-versa.

Summarizing a story is permissible as long as the story is free from forbidden acts and Sharia prohibitions.

Drawing images of animate beings is forbidden, except for what has been permitted for the purpose of educating children, or what is imperfect in creation to a degree that the animate being cannot live, or an unclear image whose features are indistinguishable.

If the questioner finds a concession regarding the drawn images or if it's possible to guide the publisher, then praise be to Allah. Otherwise, it is better to avoid working with him.