If the guys are wearing Black suits I am told that they should wear shoes! About the guests, I say let them wear what they want! For the bridesmaids, I was just a bridesmaid a month ago in Santa cruz CA on the beach and we wore dressing mid calf and we went bare foot. The thing is I have been on the beaches in CABO and yes they are rocking and I had to wear shoes on some parts of the beach. So, what I was thinking is to maybe find some really cute sandels, at least for brides maids, flipflops I dont like with longer dresses. I hope this helps.