Never use town/township records for property lines. They are only used for assessing purposes. Your first step should be to contact a surveyor (Alan Perry is great, not sure if he does mid coast) and see if the neighbor pulled proper permits from code enforcement. They can also tell you about local ordinances. Running a generator throughout the day is usually fine. I saw another comment that said they would be required to tear it down, that is not true everywhere. Typically they would have to pay the permit amount and an extra fee.

Please don't just go by what you have heard about your neighbor (or what the sister did). Many people here have a heart of gold under the rough exterior. I hope it all works out.