Pruning white pines
Topping trees is not a recommended practice. Wood rots are more likely to be a problem in topped trees. These trees want to grow about 80-100 feet tall and about half that in width. Trying to keep them smaller than they want to be is an unending job for you and a stressful, weakening experience for the tree.
They should be evaluated by several certified arborists for an onsite diagnosis, if they are a hazard, and the best way to proceed. They can let you know if their fall would threaten people or property. You can search for a certified arborist at www.treesaregood.org
Here is a link on deciding When To Remove A Tree http://extension.umd.edu/node/2273