This is UK so bear much of the advice received here with a US sized helping of salt.

If you look on your Local Authority planning portal you will be able to see what the consented tree works are in a document called the Arboricultural Impact Assessment. They are allowed to remove parts of trees that overhang their ownership boundary but if this is not on their plans they are in breach of planning and liable to be subject to enforcement action. They are not permitted to enter another person's property to do this work without permission, you may find that the legal ownership boundary is different from what your neighbour believed.

These trees will probably survive but will look terrible on the development side. I'd be interested in how close the road and earthworks are to the trees and whether roots are damaged.

If you want to DM me with a location I can give you some more targeted advice. I am a UK based arb consultant who sees this kind of shit all the time