If you set two lights of equivalent output to half power, each 8 feet from the subject, with the same modifier, they will deliver essentially the same light. How you place them will determine whether there is overlapping or individual light sources on the subject.
Practice at home with one light. If its 8 feet from the subject with your chosen modifier at 1/4 power take a test shot, 1/200 or whatever your camera max sync speed is, F8 and ISO 400. If its over exposed stop down the lens two stops and try again. If its under exposed open up about what you think the under exposure is, say 2/3 stop. You end up at ISO 400, F10, with light 8 feet from subject at 1/4 power.
Now you have a basis for judging exposure. From there its just practice and experience.
Light meters are handy and over rated. I have one. I use it in the studio. On location I rely on experience, and the histogram on the camera.