It was impossible to keep both heads in focus because they were too far apart for the limited depth of field of the long lens (100-400 at 340mm). I took a shot while focused on the buck at f/5.6 but the image was not pleasant with the doe so far out of focus and being the closest one in the image. I also tried focusing on the doe but the buck was too far out of focus at f/5.6. The image shown here resulted after stopping down to f/9 and focusing on the doe. The buck is still out of focus but there is much more detail at the smaller aperture. The buck now serves as a nice complement to the doe in this image.
For those of you interested, the buck's antlers were not symmetrical, with four tall points on his left side and five shorter points on his right. There were two separate brow tines on the right side.