Peel and section grapefruit, removing membrane and reserving 1/4 cup juice. In a saucepan, combine water, sugar, marmalade and reserved grapefruit juice; bring to a boil over medium heat. Cook and stir until sugar dissolves. Add cranberries. Reduce heat to medium; simmer 8-10 minutes or until cranberries pop. Remove from the heat. Gently stir in grapefruit. Chill for at least 1 hour. Stir in bananas just before serving.