Hi Karyn,
Decisions, decisions - you have so much to celebrate! Unfortunately the best weather months don't necessarily coincide with the best value months. If weather is your priority, I would suggest May. This monthly typically offers a stable and warm climate. March will be similar, but maybe a bit cooler, and September will be hot and humid. Many tend to avoid September because it is hurricane season, but I love to take advantage of the great pricing and low crowds this month typically offers.
If the pricing is the greater factor, then September is by far the best value month of those you listed. March will most likely be the most popular and therefore most expensive month due to the increased amount of school children that are on spring break during this time.
Regardless of which you choose - you can celebrate all of your special occasions. Check out all of the
gifts and amenities that are available for you to make your voyage super special for your entire family.
Good luck with your decision!