easement for attached home

What is the name of your state (only U.S. law)? NY

My inlaws own a house in NYC. it's a row of attached homes/townhomes. most are 1 story, but my inlaws have one of the 2 story ones on the block.

They want to install aluminum siding to improve energy efficiency. Problem is at least one of the neighbors doesn't want to let their contractor on his roof.

I looked up the deed, but didn't see anything about an easement. should i send them to a lawyer or can a general contractor look up this info and get the proper permits, etc?

As a non-lawyer, this is just a suggestion. There may be laws that govern this type of situation regarding zero lot line, or common wall, zoning or building. I strongly suggest consulting a lawyer that deals in real estate or land use law before doing anything.
Perhaps others with more knowledge on this subject will post something here, but it seems unreasonable that you would be put in the situation where you can't maintain your own structure.
When the zoning was written that allows such construction, there should have been some allowance for this situation. Check with the city zoning department. You can download the NYC Zoning and do a search for "zero lot line" at: http://www.nyc.gov/html/dcp/html/zone/zonetext.shtml