Why does my brother ask my elderly father for substantial amounts of money 2-3 times a week for " commissary " and even have our dad send a money order to another inmates books?

The only expenses an inmate has is commissary and telephone. There is a limit on the amount that can be spent on commissary in a given week or month depending where they are incarcerated. Be mindful that since inmates have a lot of time on their hands, they become very good at tearing at the heartstrings of the loved ones on the outside who are worried about inmate's well-being. Whomever is going to be sending money inside needs to set a budget for themselves. There are a lot of extra-curricular activities that go on like gambling, etc. Most likely, there is more to this than just needing money for snacks.