These well-meaning "amatures" must be doing something right, their kids are doing a lot better on entrance exams than many coming out of public schools. My Niece and Nephew were both home-schooled and at 21 my nephew is working on his masters and my neice is already taking pre-med classes. I think they are going to be just fine.
And here are some statistics to back you up...
SAT/ACT homeschoolers:
http://www.hslda.org/docs/news/hslda/200105070.asp
Standardized test scores homeschoolers:
http://www.hslda.org/docs/nche/000010/200410250.asp