when using this letter service through inmate-aid, does the inmate reply using the same service? does it cost for them to reply? Also.. when inmates are transferred to East Carroll Phase 3 from Franklin Parish what does that mean? is early release a factor?

The inmate may replay to you with the InmateAid Inmate Response Letter Service. There is no cost to the inmate, but there is a cost to the recipient of $1.49. 

Transfers can mean a few things, but early release is not one of them. Usually it is that the inmate is "working his way down" the various custody levels. If it is that, it might lead the way to the earliest possible release date.