Italy or Ireland

Which 8 nights (what time of year)? What are your interests? Why Ireland or Italy?
One thing I will say is that you can see a lot more of Ireland in 8 days than you can of Italy. As evidence, I will point out that the Heart of Ireland RS tour is only 7 days, while the Heart of Italy is 9 (I was surprised there was an Italy so short, TBH).
If you decide on Italy, I recommend contacting Sarah Murdoch (former RS Italy guide), who does custom tours. If you take a look at her Facebook page, she had some recent posts regarding a multi-generational custom family tour that she did. https://www.facebook.com/share/p/1GUoznqhnN/

You need a car for Ireland but nor for Italy.

You don't "need" a car for Ireland, but with 9 people, if you want to travel by car, you would need more than one car.

Adore Ireland but for first trip I’d go with Italy.

With such a short amount of time I would pick just two cities in either country to base yourself in for four days each. In Italy, you could fly into Venice then train to Rome and fly home from there. In Ireland, you could fly into Dublin then train to Galway, or Belfast. The only problem with Galway is that you would have to train back to Dublin to fly home. I think Italy would be more of a focus on history, but I’m sure the younger ones would enjoy the canals and boats in Venice. In Ireland, you might get out into nature more, especially around Galway. There are certainly other towns you could choose, but these choices are fairly easy, and quick. You don’t want to be spending a lot of time getting to the next place instead of seeing the sights.

I'm assuming that the trip you were asking about last year did not happen. Do those 8 nights include the transatlantic flights? In that case, you only have 6 nights in the country you select. If that is the case, and you choose Italy, pick one city that you can easily day trip from. Any of the big 3 - Venice, Florence, Rome - are good for at least 3-4 days. Then a couple of day trips to nearby towns. Or pick 2 of the 3 and forget any day trips. It would help to know the time of year.

Any thoughts?

With your group I would suggest 2 places in Italy.

Depending which cities you choose and how you allocate the 8 nights, a day trip may be possible.

Moving that many people that far for just 8 nights is a lot of work for limited return.

Is the 8 nights truly carved in stone?

The Family Tour you contemplated previously looks so much better.

Good luck