This is a huge myth. Yeah there are kids with poor skills coming from homeschooled backgrounds, but the same can be said for kids from public schools and private schools. By and large, homeschooled kids are more likely to excel in college.
CBS News (2010)
I'm not saying that everyone should be homeschooled, but to paint homeschooled kids as being unable to do group projects is unreasonable. As for my personal experience, homeschooled kids in college have generally done better when participating in group projects because they actually prepared for the group session.