As best I know there are two Halpin branches in Greenpoint. I have no idea if they will ever match up (the other one I beleive is from Dublin and the immigrant father died in orute to US or they came after he died, not sure) I do not have much to go on myself.
I will share with you my Family Tree Maker file. If you do not have the program I will print it out and mail it to you.
In 1870 Edward age 30 & Margaret age 28 both born in Ire & they show up in Brooklyn's 21st ward Edward worked a the Morracco Factory? their Roman Catholic parish was St Patrick's on Willoghby Ave where my Mary Ann Halpin was baptised in 1866 she was married there in 1887 and moved with her husband James Warren McKenna to Ward 17 Greenpoint. In the 1888-1890 Bklyn telephone directory its lists Margaret Halpin (widow of Edward) living at 43 Skillman.
It is also my understanding that one of the other Halpin Greepoint branches also worked at the Moracco factory (I have no idea what they made there or where exactly it was).
Have you searched the census files yet for your Halpin's. Email me off list and we can compare notes and see what matches. Doreen
powers@ptd.net