You cannot apply to Fellows of CBHP as a sophomore. However, Dr. Sharpe has been known to consider applications to CBHP even this late in the year.
There are some distinct advantages to membership in CBHP and/or Fellows, which include, but are not limited to, a CBHP lounge, special classes, and community service opportunities. It is still possible to do research activities, but you will not have the backing of CBHP or UFE to find and get these research opportunities. For almost anything, you don't actually need the honors college's help even though they may offer it for many things. Most of one's college classes and probably most of their college experiences involve things outside of honors.
Unlike some other colleges (and probably many high schools), I cannot see how being in Fellows or CBHP would automatically make your college experience a notch above all others. They are just two of the more well-publicized programs that UA offers. If your son gets to know professors and otherwise gets himself known (in a good way) by those in charge of various programs, good things can come his his way. CBHP and UFE are excellent programs that I would very highly recommend to anyone selected for them, but they are not the be all end alls of a UA experience.