Ask them if they would like to have a priest come visit them. If they would like that, call the parish and ask the priest to come.
Your father’s illiteracy is not a bar to his going to Confession, but as an aside, if he is interested in learning to read, your local library should know about literacy programs, many of which are staffed by volunteers. If you all have some form of medical insurance which would cover this (I’m thinking that since your mother is disabled, you might be on MediCaid), his eyes could be checked very thoroughly for unusual problems which could cause him to have problems reading without special treatment.