should i be mad?

Let’s start this off with how my dad has my sister and I with my mom and I have two older brothers from my mom’s previous marriage. I found out today from facebook that my grandpa has been in the hospital sick for the past two weeks. I texted my dad and he told me why but I had to ask. he said he didn’t want anyone knowing. okay whatever i’ll get over that. then, come to find out my dad told my brother (my parents are divorced so it is technically his ex stepchild) this has been an ongoing thing where he doesn’t talk to his own kids for months but will have constant contact with them. maybe i’m just jealous but I feel like you shouldn’t be closer with someone else’s child vs your own? and if he didn’t want to make him mad by telling his own grandkids, why would it be okay to tell my brother? please tell me if i’m wrong or not for feeling this way!! 🤕