Barb, So, you have reason to believe that light-keeper John Langton may have been an uncle to your great-grandmother Sarah? I have some friends who are close to beingprofessional internet genealogyhounds and I will sick them on this, but we'll need just a little bit more. Do you have any known facts or guestimates on John's parents, immigration dates, his siblings and/or similar data on either of his wives? Which of the kids that you listed belonged to which wife? But first, explain why none of the names you listed on your reply to my query match any of the names on your posting about your great-grandparents, Sarah (Langton) & William Smith.
I DO have a bit more info but I'll have to dig it up. I'm writing multiple books on NY lighthouses and light-keepers and am doing LI & NYC last because more has already been published about those lights than about upstate lights.
Fill in some of the above holes for me and my research team & I will get working on it, or at least provide you with some search clues of your own to pursue in exchange for your sharing your pertinent results.
If you live in the NYC area and want to go offline & email me directly, I can tell you some places to look for data, pics & news clippings. I live too far away & the city is too expensive for me to go there very often on blind searches; but for someone who lives right there, there are several possible free archives to be searched.