Give them both the same graduation gift, even if it has to be less than what you were planning, and before your niece leaves for Africa, give her another envelope and just call it a 'spending money' envelope for Africa. Your sister and nephew should not get upset about that. I've been dealing with a mother in law who for years has given money to my kids, BUT ALWAYS gives more money to my first child because, as she has favored her own first born, she favors my first born, so I understand what your sister is going through, trying to keep things even. Though I think it's silly not to celebrate her daughter's awards and accomplishments by displaying them in her own home. Back to the favoratism, for birthdays, I don't say anything, but for holidays and spending money, my mother in law's money gifts now gets split 3 ways, irregardless of what my husband says.