Venturing back in to the wonderful chaos that is AIBU..
I have many in-laws. Widowed and remarried, and long story short I have my mum, no dad, and 6 inilaws (late DH parents split and re-married, and now new DH parents). Most grandparents have accepted our new blended family and love all of our kidS.
New DH parents having a 50th anniversary party in October. They are twats (DH would agree) and are inviting only adults to a "smoked salmon on blinis followed by WTF I can't remember" lunch, but also their 5 grandchildren, of whom only one is blood (the others are steps). The menu for the day is so un-child friendly But the 5 grandchildren must come. So they can show them off despite the fact that they have never been there for any of them for any significant part of their lives, including when their DDIL died.
Actually I have already BU and have emailed MIL saying that if they can't get their smoked salmon caterers to put on a couple of plates of plain food and cucumber slices then we will bring packed lunches to their posh do. In a spiderman lunch box. Let's see how that goes down.