The State of Michigan has a website listing courses required for graduation for public school students. This may be helpful for determining what courses your children might need for college preparation. Please check Home School Legal Defense for the requirements for homeschoolers in your state.
Lee Binz addressed what all is needed for high school credits in a free webinar. Check out
Click on Andrew Pudewa, and choose the webinar "A Homeschooler's Guide to High School Grades, Credits, and Transcripts
(with Lee Binz) - July 22, 2013.