It definitely depends on which two majors he’s trying to combine. I know many people who are doing double degree in 4.5 years and I know many people who dropped one when they realize their priorities change (don’t want to be premed, don’t want to be an opera singer, etc). It is a lot of work, but a lot of it is self directed, and professors in the college will definitely understand and in my experience are happy to work with students if they find themselves struggling. Having one Oberlin degree will take him very far and he can still take courses in either division, so unless dropping one will cause financial concern, I would definitely say go for it!