What would be typical time after probate

The letter is badly worded. They want to know,
a) do you want the money and make return (if required) to revenue yourself
b) do you want your accountant to deal with it, then give the solicitor your accountants details
c) do you want them to deal with any potential payment or return to revenue. If so there will be a fee.

Given the poorly written letter I would certainly avoid choice c.
The whole thing sounds modest enough if there are multiple nephews and nieces and their spouses. So it should be very straightforward for you to do it all yourself. Pay the CAT if you are over the €32.5K threshold and file a return but pay no tax if you exceed 80% of the threshold. These are lifetime thresholds.