Been there done that. Its my in laws. They have favored their oldest granddaughter since she was born (30 years ago). My MIL told me once that she didn't worry about us because she knew we would be okay and that she had to focus on D and the girls. Now, they are focused on her kids. My FIL said once to me that the silver would go to K because he was the first grandson and carried the last name. I said "First, K is not your grandson. He is your great grandson. And second, who the hell is my son, Chop liver??" Last time I checked, K's last name was not the same as ours." My FIL got red in the face (because he forgot about his only grandson) and said "oh yeah" turned around and left. I told my husband this and boy was he pissed.
I have resented my inlaws because of this and many many other things they have done regarding this subject. I can't tell you how much money and trips they have spent on these kids and not on ours but they are the ones missing out on two fantastic kids. My daughter will be the first of their grandchildren to graduate college. The first two got preggers and dropped out of high school.
When my mom was diagnosed with frontal tempural dementia, I asked MIL to step up with our daughter because she was hurting so much with this and yep, nothing! How can you not help your granddaughter who is hurting? We ask them to call our DD at college and they never do.
I NEVER say anything negative in front of my kids. Regardless of how I feel, these are their grandparents and they love them. And yes, they see the difference in how they are treated as does the rest of the family.
Wow, you touched a cord here! I'm glad to know I'm not the only one with this problem.