Is it harder to be admitted to the Georgetown Walsh school of foreign service or to Georgetown college ?
And once in a certain college, can you take classes at another college?
It’s a bit of an apples to orange comparison to say which school is harder to get into, but the SFS has a pretty self-selecting applicant pool. In any case, you can look at the admissions breakdown by school at https://georgetown.box.com/s/xani81o0z2iq0anudhge (the 2017 profile is under development, presumably).
Generally speaking, students can take classes across schools, although some of the more advanced/specialized courses (especially business and nursing/health) are restricted to certain schools/majors without special permission. Most courses in the College are open to everyone, and I would say the SFS has the fewest classes ‘in the SFS’ or limited to just its students. In fact, most of the SFS core curriculum and requirements is technically made up of courses ‘in the College’ and listed under departments like history, philosophy,theology, economics, sociology, foreign languages, etc. So it’s pretty porous.
There are some limits though to the extent to which you can cross over between schools. For example, you can’t minor within the College if you’re enrolled in the SFS.