Possible affinity groups might be:
Clans - visiting the ancestral clan lands and meeting with Clan Chief
Distillery - a fun tour for those interested in the making (and drinking) of whisky (Scotch) and whiskey (Irish)
Family reunions - exploring areas from which the family emigrated, meeting with relatives still living in the area
Genealogy - with research times arranged for you at government facilities and libraries
Golf - play it or watch it... with over 900 courses between Scotland and Ireland, there is something for everyone
Musicians - several major musical events, famous worldwide, take place in Scotland and Ireland, including Pipefest, a gathering 20,000 Pipers, Pipe Bands, Drummers and Clansmen in Edinburgh, the World Pipe Band Championships in Glasgow, and the Royal Edinburgh Military Tattoo.
You can form a group of friends or family just for traveling and sightseeing, incorporating some or all of the topics listed above. A group can be whatever you want it to be with the assistance of Celtic Journeys.