Steps/Halves And Weddings

My nephew (from brother #1) is getting married for the second time. All 4 of my kids (steps + natural) were invited to the first one. In the meantime, my niece (from brother #2) got married and only invited the natural kids who chose not to attend because their brother and sister (halves) were not invited. I TOTALLY respected their decisions. I sat next to my nephew in the church and told him my two children were not attending because my other two children (steps) were not invited. He concurred with their decision not to attend. NOW nephew is getting married again but only invited my two natural children and not my step children because they were trying to cut costs. I am heartbroken. I will go to the wedding, but, again, my natural children will not because their siblings were not invited. Are we out of line?