Obsessed fil

Okay so long story short, my father in law is OBSESSED with his son who is married to my sister. I mean obsessed. He has framed pictures of them together, he always talks about him, always posts pictures of them two on fb, everything my bil does my fil PRAISES him. He has two other children (my husband and a younger daughter) he rarely says anything about them and if he does its about the oldest son doing or having something similar. When my bil goes on deployments he won't visit or even call his grandkids. But if my bil is around he is always taking pictures with them or playing with them but as soon as my bil walks away he stops. Everyone sees it but doesn't have the nerve to say anything I guess. But any way, my bil just made Chief and my fil is flying out to go see him. He put on fb how he was going to "pin" my bil and blah blah. My sister calls me and is upset because she thought she would be doing this. When she confronted her husband he was kinda like yeah my dads gonna do it, and she just felt heart broken. They have been married 16 years and have 3 kids and his dad comes before them. Are we wrong to think his wife should be the one to pin him?

How could she confront them both? Its a super freaky obsession and my bil just tells my sister hes my dad, he just loves his kids and we wouldn't be the people we are today blah blah. My husband knows I think its weird and when he became a police officer he asked if he could be the one to pin him and he said no that I was because his wife. And he was bothered and left early. I'm very straight forward and let my husband or in laws know when I dont like something (I'm not a bitch but when shit gets weird I'm like nope step back) (example: when my husband and I got our life ins, he straight up asked my husband if he was the beneficiary of his acct. And I was like no his wife is!! Just an example of the shir he tries to pull. ) my sister on the other hand is really quiet and sweet and kinda doesn't have a say when it comes down to my fil and bil. How does she handle this?