The situation in that country has truly been messy, with respect to the business of royalty -- two deposed houses since the country acquired independence from the Ottoman empire. The monarchy has been abolished and restored several times, with some kings being recalled to the throne after being deposed. Reinstatement is highly unlikely in the future, but it has happened in the past.
Bearing this in mind, then, one has that there have been periods in European royal history when as many as FOUR descendants of King Christian IX of Denmark have been styled as kings -- correct? I say this because of the situation in Greece (i.e. Constantine I and Alexander), while their cousins were sitting on the thrones of Denmark and Norway.
Have there been other examples of four simultanous kings of the same house? Somebody already touched upon it in an earlier thread below, with respect to the house of Bourbon, which has had several offshoots and cadet branches.