It would be better for the female if you had another one. Since your ganders have grown up together they may not fight One will most likely be the dominant of the 2 and will get to mate with the female more often.I have also heard of a gander or female being shut out of the flock too if the gander and female pair up. So getting another female would be a good idea. My ganders don't fight, when they get into the pool there can be a bit or wrestling but it doesn't last one or the other usually gets out.
