A. Well, you are right that #4 plays a big Passover Seder role with the 4 sons, 4 cups, 4 biblical expressions of redemption. But there’s also 3 Matzot, 2 types of dipping, Rabban Gamliel’s 3 Seder Essentials (Paschal Lamb, Matzah and Maror), 10 plagues and 5 or 6 items on your  Seder plate depending on custom. So not everything Seder-wise has to match four .

But since you asked, here’s an answer: Rabbi Akiva was the host at that famous Seder. He had four Rabbi guests!