I am very familiar of what you're having to deal with, Most all ground nesting bees I have dealt with have two ways in and out of their nest, usually found within a couple feet from each other, There is a foam spray that you can use to fill up their hole's in order to help contain and kill some of them, however this stuff dissolves after a few minutes and it doesn't kill them fast enough before they can come at you,..... so do this before the foam fully dissolves, You can put some netting over the holes and lay boards to hold down the edge of the net down, then be ready with some good hornet spray to shoot into the net as the bee's will start slowly coming out , this usually gets about 95% of them, be sure to wear eye & mouth protection to keep from breathing or getting it into your eyes,