Control Sublevels of a Sublevel from master

Hello,

I have Master level which include Map1 sublevel which have his own sublevels Map1Sub1 and Map1Sub2.
The question is how can i control these sublevels from Master level? I want to be able to load/unload visible/invisible them from blueprints in Master level. Where i dont want to make them sublevels, i want to hold them childs of Map1.

Is there any possible way of doing this ?

Thanks!