Grandfather wants us to pass on the name

My husband and I dont know if we’re having a boy or girl yet, but we already have a name for each that we love. We’ve known these names since before we even started trying for a baby, they are damn near set in stone we both love the names so much. My husband is a Junior, named after his dad. His dad goes by the first name and my husband goes by the middle name. Our boy name would carry on the middle name, as a nod to both of them, but we have a different first name we like. My older brother’s middle name is our dad’s first name, and i liked that it was a less intense way to honor him. All our conversations with FIL about it have been lighthearted and playful, but he has repeatedly expressed that he would really like for us to name our child, if it’s a boy, the same name. As in, he would be ____ the third. And i just cant stand the thought of it. It’s such a mouthful, and no offense intended to anyone who has a third in their family, but the only thirds I’ve ever seen/heard have been very snobby douchey rich my-daddy-will-sue type dudes. I wouldnt know what to call him, because both the first and middle names are already taken, and FIL suggested “Trip” as in short for triple 💀 Is there any way to softly but firmly get across that we wont be doing that ? It comes up damn near every time we talk about the baby. I really love the name we picked, and part of why i came up with it is because I felt like it was a nice way to honor both my husband and his dad, who has always been an immense help to us. I want to honor them but still give our child his own unique identity.