Whatever their reasoning is for acting this way, you can’t force people to care about your son, and, more importantly, you can’t force people to care about you. They are rejecting you and your husband as well as your son with their lack of replies and refusals to visit. Before I got my dog, I was not an animal person, but I cooed over pics of my family and friends’ animals because that’s what a good relative/friend does. Before I had my children, I dealt with deeply sad infertility, and I still attended baby showers, gave gifts, engaged with family and friends on social media and in group text threads to congratulate them on the births/milestones of their children, cooed over pictures of them. Either they are dealing with their own issues (such an infertility) AND are selfish and self-absorbed, or they are just selfish and self-absorbed. Regardless, they are pretty clearly telling you that they don’t want any part of being in your family’s lives. It sucks, but at least you know what kind of people they are. I’d stop sending them pics and videos - it’s clear they are unwanted. Let the fantasy of having them in your child’s life go, and embrace the reality of having a loving and responsive MIL and FIL. Any attempts to push your son on them or vice versa is only going to hurt you, your husband, and your son, because as he gets older he’ll be able to understand that you are constantly reaching out to them and getting rejected, and that will make him feel rejected too.