Older siblings kids = grand parents "favorites"

I'll try to summarize but I may fail because it's been years of this. My sister is older than me by 9 years (I'm 25 now) She and her 2 kids lived with my parents until 3 years ago. Her kids are now 10 and 15. I have a 3 year old and am due with my second in a week. My mom is in stage 4 renal failure and has health issues. My entire life felt like I was a second mom to my niece and nephew and that since I was a minor and lived with them, I was constantly pushed aside for them. I worked and eventually moved out at 16. My parents constantly have one or both of my sisters kids on the weekends. I live 10 minutes from my mom and my sister lives an hour away in a one bedroom apartment. So my parents always are always helping my sister. I'm lucky if my parents see my son twice a month and we live right by them. When they do stop by, it's ALWAYS when he's napping which is always 1-3pm and they know this. There is so much I want to add in here but for the sake of length I'm trying not to. I feel like since my mom has been sick and because of my sister not working up until the last year, my parents pretty much forgot about being grandparents to my kids because they're focused on parenting my sister's. it kills me... I called my mom today to see if they wanted to come over but they have to take my niece back to my sister so I didn't even bother. I really wanted to tell her how much it hurts to be cast aside regardless if it's because my sister slacks in parenting. I'm their child too and my son should matter equally... and I know when this baby comes it'll be the same. 😔 i don't take my son to my mom's because my brother smokes inside their house so it's not healthy. I feel like it's like a huge "fuck you" for actually raising my children and not relying on my parents to do it... anyone else have a sibling that has overshadowed them all their life even if it's because of their screw ups?