Have you talked to your sons counselor about this?
At most if not all top private schools, college counselors are very accessible and mostly know their stuff.
Additionally, which Penn school is the legacy from and is there parent involvement at Penn either financially or with time?
Seems to me that Harvard REA will probably not workout as is it just too competitive for someone with a stellar application that is not a URM, Legacy or winning INTL competitions etc.
Wharton, the lack of anything business ec will hurt though if the legacy is Wharton undergrad it is worth a shot. Otherwise what about going Penn Arts and Sciences ED?
Your son should have enough to get him and legacy will help him stand out. Additionally, Penn is very pre-professional and lots of Investment Banks and Consulting Firms recruit both Wharton and CAS.
Someone who was motivated enough to have this stellar of a resume should have no trouble taking advantage of the job recruiting opportunity whether he attends Wharton or CAS.