Formal Attire: A little less formal than black tie, but still elegant and sophisticated. Pops of color welcome, tux not required. Women in floor length gowns with elegant jewelry and refined clutches.
https://www.theknot.com/content/formal-wedding-guest-dresses
Black Tie: A black tie outfit is built around a dinner jacket, a dress shirt, formal trousers, a bow tie, and polished dress shoes. For women, we can generally assume that “black tie” equals “long.” But that doesn’t mean just any long dress fits the bill. Make sure your dress is rendered in an evening-appropriate fabric: think velvet, chiffon, silk, or lace.
https://www.marthastewart.com/7912329/what-it-really-means-to-plan-black-tie-wedding
For the welcome party and brunch, we recommend smart casual/ cocktail attire. Think "garden chic" so maxi or midi summer dresses, jumpsuits for the ladies. For the men, chinos, collared shirts or suits. The welcome party will be outdoors in the shade and the temp is expected to cool a bit in the evening. Consider linen, cotton and other breathable fabrics. We will provide hand fans. The brunch will be indoors, and we recommend similar attire.