Oh, That is great news for you. I was wondering if the people you are looking for died in the town of Boonton, For burial plot I was able to get certf from the Municipal Bldg. If they died in Boonton, or surrounding towns, Hanover Twp, ect. My info was yrs ago. Also it's a trip, even for me but Trenton Archives I found my Dolan's 1884 death certif.
Good Luck, I know what your going thru, even been to Ireland