West Ireland!
I visited with my mother in 2015, and there are a lot of gorgeous rides there (and options for short non-expert horse and/or pony adventures for the non-horsey crew if they have interest)
There are many castles for visiting, as well as beaches, walks to old churches, and incredible views. Connemara is a beautiful part of the country, and even on days with nasty weather, we never failed to see a rainbow during that leg of our trip!
Galway is a really nice town, and not much of a city at all, but has some cool museums and great restaurants if you do want some more urban activities, perhaps using a spot on the outskirts of town as a base could give a good compromise between being in the middle of nowhere and having a larger variety of options for the non-riding crew.
Willie Leahy is well known for his day-long rides in Connemara, but I know there are few hunts in the vicinity of Galway as well.
A couple other activities we really enjoyed in Ireland were kayaking (there are short and long guided trips on lough corrib and galway river, if you do choose to focus on west Ireland)
We kayaked in Kerry with Outdoors Ireland (a fabulous company, I’d recommend contacting them if you end up in their neck of the woods, their owner, Nathan, was the consummate host and tremendous fun when we spent an early morning kayaking with him)
We also did a falconry walk at Ashford Castle, there are a couple different locations in Ireland that offer falconry hikes, and the one we did was incredibly cool! Highly recommend if you can swing it.
Also for what it’s worth, if you aren’t experienced at driving on the other side of the road, Shannon is a much more friendly airport to navigate than the Dublin airport (not to mention Dublin itself).
As for food, Ireland is not famous for its cuisine, which actually makes it a great choice if someone with you needs bland options! I don’t think we were ever in even the smallest town where a ham and cheese sandwich wasn’t on offer, soups were typically quite ordinary, and beef-and-potato dishes are mainstays for sure.
West Ireland is famous for seafood, so if anyone in your crew is an adventurous eater (or just likes seafood), they may be very happy campers indeed! But even at places right on the ocean, in oyster season, every bar had burgers and sandwiches on the menu as well.
I highly recommend the Rick Steve’s guide to Ireland for it’s guided drives and not-overly-touristy focus, we used it as our primary source in planning our trip, and loved our time there.