Help with determining guest attire

Hey everyone!
I’ve been having a hard time deciding on an attire wedding guest should wear. I asked FH and he said tell them wear their Sunday best and I started cracking up telling him that’s not one of the attire options lol. But we are getting married at a banquet hall we have the choice of using the indoor chapel or outdoor garden for the ceremony and reception and cocktail hour will be held in a lovely banquet hall. Our wedding starts at 5:30-11:30 so we know casual is off the table. Bridesmaids have long chiffon or tulle dresses from Birdy grey. And we are contemplating doing tuxes for the groomsmen. The dress I want is a simple yet elegant mermaid sweetheart neckline with a tulle skirt. We just want something fitting of the atmosphere and what we will be wearing. FH wants guests to be comfortable enough to dance in their clothes. I can’t decide between semi formal, cocktail attire, formal/black tie optional.

Thoughts?
Thanks!!