Juggling the personalities of very different people is so hard sometimes. If it was me, I would not mention these things to your son. I WOULD start a journal of these things - what the reaction was, when, over what issues, etc... I would just keep it secret. The reason for this is that sometime in the future there could be a divorce. This kind of thing might be a record that your son would need to help keep his kids, or you might need if your state has grandparent rights. I know in my state a grandparent only has rights if there is a divorce. My parents needed to use this as the stick with my bro's ex. They used a whole lot more carrots, but ex sister in law knew that if she tried to keep niece away, the court would look favorably on my parents and force visitation.
Just keep a private record in a place your son will not see. Then, if he later needs it, it exists.
As a parent, sometimes you have to learn that no grandparent is better than a bad grandparent. We pretty much cut my inlaws out of our kids lives. NOT because we wanted to, but because their blatant disinterest hurt our kids. We keep in touch with hubby's dad and stepmom, but we really only see them on holidays. Hubby's mom, well, for me she does not exist. She has been so awful on so many occasions - far above rude, doing things that could physically hurt my children if I allowed it (insisting on lit candles on the floor with a 1 year old toddling around? that was the LEAST of what she did), and really going out of her way to emotionally hurt our kids, to show them that they just don't matter.
At some point, your son may have to realize this. Until then, you need to just not comment and be an easy presence in your grandkids' lives. My parents did a couple of things that really helped them be constant in my kids lives. One was to have a special saying that they repeated at each visit or phone call. My dad was "always remember and never forget that Grandpa loves you". My mom had different things with each kid. My dad read the old Uncle Wiggily stories onto cassette (back in the dark ages, lol). The kids listened to those every night as they fell asleep - for YEARS. My mom made videotapes reading stories to the kids. They got the video and the book. Those tapes absolutely were worn thin - they were bigger favorites than Barney or Blues Clues - and that is saying something with kids born in the 90's!
Focus on what you can do for grandson. If they plant the idea that this place or food is bad, find another favorite. There are tons of restaurants and you will find many to focus on. Keep the focus on having fun with him, let them worry about the competition and other BS.
Oh, when my oldest was little my dad suddenly decided that the hot water tank would have to be drained every so often. Usually on cool days (November here, usually) when it was too cold to use the kiddie pool. Grandpa would hook a hose up to the hot water tank and fill the dang kiddie pool with warm water. I remember the first time I came to pick up Wiz and he was in that kiddie pool on a chilly evening. My parents and one of their friends all had their pants legs rolled up and their feet in the water too! I just laughed (they thought I would be shocked and upset, lol) and rolled up my pants legs too! We had a wonderful visit and Wiz tired himself out enough that he slept that night. Find stuff like this to do, stuff that is unique to you. Your grandson will grow up remembering one set of grandparents who placed ridiculous demands and one set who just loved him.
Then, if there is ever a custody issue, you have your records AND a solid relationship with grandson.
