Glad I could help. 
As for the GUI mouse clicks, I did it like this:
Code: ags
Edit: Minor syntax corrections.

As for the GUI mouse clicks, I did it like this:
// main global script file
int guimb; // stores mouse button clicked on gui
function on_event(int event, int data) {
//...
if (event == GUI_MDOWN) { // if mouse clicked over a gui
if (IsButtonDown(LEFT)) guimb = LEFT; // if left mouse button pressed, store it in variable
else if (IsButtonDown(RIGHT)) guimb = RIGHT; // if right mouse button pressed, store it in variable
// and so on...
}
//...
}
function interface_click(int interface, int button) {
//...
if (interface == GUI1) {
if (button == 0) {
// do stuff
}
}
if (guimb != LEFT) return; // only allow left mouse click on the following guis:
if (interface == GUI2) {
if (button == 0) {
// do stuff
}
}
//...
}
Edit: Minor syntax corrections.