UW pre-science would be an easier admit than engineering. Note that math and physics are not direct admit and are capacity constrained. Here’s info on the secondary admission process for these majors:
Math: Undergraduate Admissions | Department of Mathematics | University of Washington
Physics: Admissions | Department of Physics | University of Washington
edit to add: I see you mentioned some CS interest. Note that it’s virtually impossible to switch to a CS major at UW. He might consider schools that have a more flexible entry into CS once he is a student.