Go here: http://www.itd.nps.gov/cwss/
click on soldiers, put in the last name (you should do this with all possible spelling variations - including Feagan), do not put in a first name, do not put in a unit number or function, but do click on Mississippi. I think you will find most, if not all of your men here. After getting this list, look here:
check the county they were from and even surrounding counties, and see if some of these men don't match the units raised in those counties, and you will be almost certain you have found them. You can then order their service and pension records here on the board by clicking the box at the top of the page. Good Luck!!