1. I would suggest my neighbor set up a camera to see if it could be squirrels instead.
2. I have seen American and Fish Crows all around Monmouth County, NJ.
3. I live where there are mainly crows. I haven't been able to observe a nest though.
4.The owls that would take over their nests. Other birds that would live nearby that would be on the lookout for bigger prey. Such as the eagle that lives nearby. I have seen crows try to chase the bigger birds away.