Lucas,
There are few things as rewarding as owning a family gun. Your granddaddy must have thought a lot about you to leave you his guns. Are you a hunter or target shooter or both? These old Parkers can be used with appropriate loads.
www.rstshells.com makes the best I have ever found. I reload most all my shells, but when the occasion dictates I call RST. There are members here that can make a hammer screw for you. I just don't recall who they are.
Best of luck, Harry