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Do you know the variety of the tree? There are several species specific diseases that might cause this, but I need to know the species to investigate. If you can send me the type of pine tree it is, I should be able to give you some direction in what might be killing them. If you would like, the University of Illinois extension office should be able to help you as well. This is their website: http://web.extension.illinois.edu/dupage/?CFID=37476861&CFTOKEN=38157422

Pine cones are constantly produced throughout their lifetime, with peaks in cone production about every 3-5 years.

It really should have stopped by now. If it is still weeping sap, this means it likely has an issue with the cut. I would ask your neighbor to check the cuts and see if one has a fungus infection or a pest problem. As a precaution, he should treat the cuts with a fungicide.

It is hard to say without seeing the trees, but it does sound like they have a problem. If they have been healthy up until now, then you should check for environmental changes that could be making them ill. Things like new construction or plantings can divert water and nutrients from the trees. Has there been any changes like this near the trees? We recommend that you have a local arborist come and look at the trees. He or she can better give you information on what may be wrong with the trees.

If it is turning brown, it is dying. This article will help you determine if it is still alive: https://www.gardeningknowhow.com/plant-problems/environmental/how-to-tell-if-a-plant-is-dead-and-how-to-recover-an-almost-dead-plant.htm

Do you know the variety of the tree? There are several species specific diseases that might cause this, but I need to know the species to investigate. If you can send me the type of pine tree it is, I should be able to give you some direction in what might be killing it.