Welcome John, it's great to hear you have some family guns.
DO NOT put a screwdriver to your guns unless you have the proper tools and know what you are doing. Otherwise you risk ruining the screws. Stick to VERY light application of oil on the metal with a rag and some diluted murphys oil soap and rag on the wood. An old toothbrush will help get the years of crud out of the checkering.
John where abouts are you located in NH? There are several knowledgable members in NH (and John Dunkle
). A few of us shoot at Major Waldon's on a regular basis and it would be an easy place to meet. Bob and Scott could measure up your barrels. There are also a couple of gunsmiths some of use who are familiar with doubleguns. PM me and I'll fill you in.
I didn't see this until this morning (yesterday I was in Ilion, imagine that).