Read to the 2 year old. Work on letters and numbers with the 3 year old, perhaps do kindergarten (Calvert) and phonics (Sing, Spell, Read and Write). Depending on what the 5 year old knows already, he could share with the 3 year old or do more advanced reading, writing, and math.
The older ones are more difficult. Learning style (visual, auditory, or hands-on) changes what curriculum and/or method will work best, and depending on how deficient the schools have been, they may need some remedial phonics / math / writing to catch them up on the basics. History, science, art, etc. are of secondary importance, since those will be much easier to learn once the basics are in place. I recommend Saxon for math up to whatever level becomes difficult to understand (in my case, Advanced Math), and reading is easily taken care of by giving them interesting classics, such as Chronicles of Narnia, The Hobbit, Lord of the Rings (or if they really hate reading, comic books and popular fiction until their reading skill increases), then having them communicate the basic plot line through a verbal or written report. They could also take turns reading out loud with someone nearby to correct pronunciation.
It's hard to say anything more without a good deal more information. But here's a link to the Idaho legal requirements for homeschooling (I assume the family is in your state?)
http://www.chois.org/law.html