We're doing pants with short sleeve shirts - that is just my preference. We told FI's guys and they are all OK with it. Honestly, I think shorts is just too casual, but if you are OK with it, then do what is best for you.
I found tropical weight trousers and nice shirts at this website:
TravelSmith*Travel Clothing, Travel Accessories, and Luggage from TravelSmith Outfitters so the guys don't need to wear shorts to be cooler, since the fabric of the trousers is lightweight. Plus, with a 5pm ceremony on the beach and the breeze, it's not like they'll be roasting. They can make do. FI is wearing a suit! (his choice) At least I didn't make them do that. LOL