Do you mean is it possible for one 'soul' to have been both a man in some physical lives and a woman in some other physical lives? This is surely possible and even common. From what I have gathered, it's more uncommon for someone to be exclusively one or the other in all of their lives.
If on the other hand you are asking if one 'soul' can be in two living individuals simultaneously you are asking a much more difficult question. Individual identity is a very sticky question even for the sciences, let alone for 'metaphysical' systems where there is nothing to test. I know that Edgar Cayce asserted that certain 'individuals' had simultaneous incarnations in the early days of human life on earth, but that it had become too because of the increasing 'entrapment' in the physical world.