The concept that everyone is descended at one point from everyone alive collapses at a certain point in time because of the difficulties of transportation in early times. It is probably more accurate to say that a person is descended from all the persons living in a particular local area than itis to say the whole world. In fact, because the number of your ancestors doubles with each generation you go back, the greater likelihood that some of these ancestors will show up many times in one pedigree. It only takes about 275 years, roughly eleven generations, to arrive at the point where one person has over one million ancestors.
Queen Elizabeth II has no Byzantine ancestry. Her husband Prince Philip, however, is the grandson of King George I of Greece whose descent from the Palaeologus Dynasty of Byzantine emperors is well documented.
The term "gay" carries modern connotations which might not fit ancient ones with the same precision. An Athenian male citizen could have a younger male lover, be married and have children, and go out and drink with Heterae in the evening. He was eramenos, the "penetrator" (of just about anything). Instead of a term such as "gay" you may want to consider a scale with extremes at either end in general (in which Plato probably tended toward one). These options were available and potentially acceptable for urban male citizens of Athens.
