yes that's my understanding too, two of the same gender and one of the opposite gender. However that's only a tradition, not a requirement, in reality the parents can choose to do whatever they wish.
I believe that in the Royal Family, some children have many more godparents.
Yes, i agree with daisynonna and woifgang. Traditionally, 2 of the same sex and one of the opposite, although you can actually have whoever you like and as many as you like.