Due to the abundant misusage of the term 'illiterate' (as a deriding word), I think it is hard to use it without sounding condescending/insulting. How about using "uneducated" or "unschooled" instead? However, the exact meaning of these terms, too, can be vague. Hence, I would say the best way to address this group is by using an entire phrase, instead of a single term, to indicate what you exactly mean.
