I just have 1 simple question??? How do you get 2 textures on one brush without making the brush hallow???

im not sure if this ur question but press control shift on the brush, instead of just shift. so click both control and shift and point at one part of the brush where u want that texture to be and another part of the brush using a different texture

ok, this could be super obvious with what shadow just said ,but you cant click twice with the ctrl + shift click thing, you have to select all the brushes you want with one click.

And to go back to simple English:

To texture a single face (or to select a single face to be more accurate) hold down Ctrl and Shift then click the face you want to texture; you can then apply a texture to a single face.

Seen as you've brought this up; remember to build using the system/caulk texture then texture visible sides only.