I wonder how many people never answer because of this business of logging in.Personally it is annoying, That being said.
While there were Dorlands in MOrris/Sussex/ and Warrnen Counties, the names changed to Durling was done by Clerks and not by the actual family decision to do so.I think that they simply gave up and went with it.The same with Darland in Kentucky. They spoke a form of Dutch-English in those days, and most clerks were English-probably familar with their Irish neighbors, so they used the familar rather than the correct spelling.
I agree with you that because of the name Alexander which is very Irish/Scottish that your Durlings most likely were Irish Durling or English Darling's.Many of the residents of Sussex and Warren were Loyalists and went to Canada for a time and then down into New York and Northern and western PA.Some Dorlands did this also, some remained in Canada. I would not get so hung up on Dorland that you guys miss other surnames.It is the right thing to do to check out all the other possibilities.We have had to do that with our research also.There are some lose male Durlings/Darlands in the Ohio/ Indiana area who we have had a difficult time matching up, simply because they seem to be alone.Once the Rev. war was over, young men took off with their new found friends and left home, where before it was groups of family members traveling together.You might recheck the neighors in the census records and then see if possiblly you find these names in the NJ/PA states as well.
I also suggest rechecking the Sussex County area as well as the Minisink NY area because they with Warren County all were lumped together as the NJ/PA/NY line moved back and forth.There is a good site available. Also the Northampton, Pike County areas border and are included in this area.
Sorry I have no more helpful information at this time, but I agree Durling in your case is Irish.