to answer your question it would be good to know some more details.
What are you interested in? Landscape? Sightseeing - stone age things,
castles, gardens, churches.....? Walking?
Do you have some special points you want to go to? Dublin? Northern Ireland?
Perhaps you have some family connections?
My first idea was renting a house for such a group of people. But that will depend on what you want to do - 'cause you wouldn't love to drive all day in Ireland. :-)