Wedding guest groups

That's a tiered reception and it's widely frowned upon as far as etiquette goes. Anytime you make some people more important than others, there's a risk to hurting feelings.

Some couples do prefer intimate ceremonies with immediate family only. But, if on the same day, you serve a full meal to certain guests while serving snacks for others, it makes it an obvious and offensive tiered reception. If you eloped on a separate day (you two + 2 witness), then had a bigger celebration of marriage reception later, that is more accepted. Do note that a cocktail reception can be more costly than serving a full meal due to grocery and manual labor costs creating large batch small hors d'oeuvres.