How to connect 2 vga projectors to 2018 Macbook Pro

to selectively mirror certain displays, use

System preferences > Displays > Arrange

Each blue box is an Icon, and they can be re-arranged, and the Menubar icon can be as well.

Drag a display Icon you want to be the same as another over the other, and they will merge into a slightly overlapping mirrored set.

You should be able to do a "test run" with one display and the Internal, just to see what it will look like. I don't have a screen shot handy that shows this feature, but it should show them nearly-overlapping, so that you could still drag them apart again later.

You can use two adapters in two ports and [√] Mirror displays.