Could someone claim their step-son in law as a dependent if they meet the gross income requirements?

The scenerio:

"Ed has supported his stepdaughter, her husband and their child since his wife's death three years ago. Ed promised his late wife that he would support her daughter from a former marriage and her daughter's husband until they both finished college. They live in another state and each make less than $2,000 of gross income per year. Is Ed entitled to dependency exemptions for the three individuals?"

Use supporting IRS codes, regs and court cases to back up answer.