We have always requested and received a daybed, but I do always request. Especially with a family of 5, I think you will not have a problem getting a daybed.
Things I love about the Beach Club....The easy walk into and esp. out of Epcot at night (when all of the other people are heading towards the front of the park, it it so easy to walk out the "back" entrance"), access to great Epcot restaurants, Storm Along Bay, Beaches and Cream, walking over to the Boardwalk, we have always had great CMs and if there was a problem, they have been prompt about responding. My sons really like MGM as well and the close proximity of the Beach Club to MGM is a plus.
Have a great trip....we will be there on the 8th. Single Digits now!