Doug, thanks for the question. Whitetail biologists say that as for the sex of all fawns born each year across the country, it averages out to be about 50-50 buck/doe. To the heart of your question: No, it is not unheard of for a doe to have 2 buck or 2 doe fawns. But at the end of the day, in a herd anywhere, it averages out to about 50-50 buck/doe fawns.
More about deer fawns: Top whitetail scientist Dr. Grant Woods says that in a normal herd, a doe giving birth to twins is the norm. In a prime habitat where the soil/feed/cover is outstanding and there is not an overabundance of deer, 20% to 30% of the does might drop triplets. But in a habitat with poor soils and feed, a stressed doe is lucky to have and raise one fawn.