You don't say what ages they are, or how they differ. Are these teenagers or is one of them a toddler? I only ask to make sure its favouritism / sexism on Granny's part and not just because she thinks bigger/younger kids need more attention. Can you afford to match most of that amount and put it in a bank account for your step daugher? If so, then no, don't make an issue yet. You've probably done this already, but just huddle up with step daughter and tell her how unfair it is and how proud you are of her for staying silent when Granny is such an outrageous old sexist. Tell her she is growing up just fine but you are worried about her brother never growing up at all if Granny suffocates him into being a spoiled baby all his life. Make the kid feel she is stronger, special, appreciated; not alone and not really being sidelined - that someone is watching and thinks she's great. Your secret. Maybe you two could even develop a secret language of eye rolling and nose tapping for when Granny is off on one of her displays. Don't blame your wife - she probably got the same cold shoulder from her mum and is more concerned with not rocking the boat.