children in college abroad, how it affects EFC and Aid?

Your ds’s would be better off looking for schools where he would qualify for transfer scholarships or low cost schools.

These links are older, but you could start researching here:
http://talk.qa.collegeconfidential.com/financial-aid-scholarships/1651944-very-low-cost-oos-coa-universities-less-than-25k-coa-for-everything-p1.html
http://talk.qa.collegeconfidential.com/financial-aid-scholarships/1473219-research-universities-with-lowest-oos-tuition-p1.html