Since your dates coincide with the President's Day holiday, you'll see some crowds during the week of your visit to WDW. Many schools (including the schools that I grew up going to in Rochester NY) let out for this week. Many families take advantage of this school break to take a vacation and head South to warmer weather. Just get to the parks early!
Last year, February temperatures for this same week ranged from highs 65-84 and lows 39-62. So my advice for February is to bring layers. Weather for a day at the beach is likely however you might want to wait until you are in Orlando to plan which day would be most appropriate.
You must celebrate your daughters birthdays in WDW! It's the year of Celebrations, after all. WDW has unveiled a "What Will You Celebrate" theme for 2009.
Consider ordering a birthday cake, In Room Celebration decor and gifts or planning a special event such as a fireworks cruise. Here's a
link to give you lots of incredible ideas.