You may be able to get what you want by using the hyperfocal distance.
With that camera at f/8 and a focal length of 35mm, the hyperfocal distance is 18 feet with a near distance of 9 feet. I’m not familiar with that lens so I don’t know how easy it will be to prefocus the lens at 18 feet; the distance scale on many lenses isn’t very usable. Perhaps you can use autofocus to focus on something 18 feet away then lock the focus? Make sure the people are no closer than 9 feet when you take the picture.
I've erred on the side of caution for the DOF circle of confusion. Some DOF calculations will show distances that are 17 feet and 8.5 feet.