Is there a way to subtract multiple objects from one using single boolean modifier? For example I have a wall, and I need to make multiple holes in it for windows. I wanted to parent an object that will make a hole in the wall to a window object, so wherever I move the window, the hole will be made automatically, and if I duplicate the window, the object that is it's child will be duplicated too, and will generate holes too. Thanks in advance.
No, you can't input multiple objects into a single boolean modifier.
You can add as many boolean modifiers as you want though. Simply create multiple boolean modifiers with their respective object's input.
You can also join all objects into a single object and use that as the boolean input. E.g. you could duplicate your window, then merge it into the boolean input object by ⇧ Shift RMB selecting the input object (making it active) and pressing ⎈ CtrlJ to join them.
As you intend to speed up the process, I'd advise you to use the built-in BoolTools addon, which creates a shelf for assign boolean quickly.