Child maintenance

Me and my husband have a special guardianship order for our grandson. His dad has never met him, contacted us to ask how he is or engaged with social services when it was going through court. My husband thinks that we should pursue dad for CM. I don’t want anything from him as he has never bothered with his son and we are bringing enough money in to not need it. My husband says it’s the principle for his dad to financially support his son. I’ve said if that’s the case we should pursue CM from my stepdaughter who has only ever given us money she owed us for stuff we bought our grandson when they both came to live with us. Neither of them work and are both on benefits. My SD never has any money and is constantly asking her grandparents and her mom to borrow money for food. She gets more money in benefits than my husband does wages. I don’t know anything about dad’s benefits other than he gets them. I don’t see the point in going through the CMS to get a pittance from either of them and then have mom asking people for money because she’s had to pay for her son. Am I in the wrong in saying there no point going for CM as either: 1. They won’t pay or 2. We don’t need the money as we are financially stable enough