It is impossible to be in more than one guild at the same time. If you wanted to have another guild made branching off your original guild (such as Mount Olympus Mark 2) the only option left is to have a friend lead the new guild. You could still transfer fg to one another to purchase amenities for the new guild. You can both work together to run both sides of the guild.
Unfortunately, I do not see the feature you suggested being implemented anytime soon. I believe my suggestion would be the next best thing