Austrian pine needles live for 4-5 years before dropping, so each year you will likely see about 20% of all the needles drop. With 4 mature Austrian pines, this is indeed a lot of needles.

CSU encourages homeowners to leave pine needles under the tree as a mulch at a thickness of several inches. They can also be used around permanent landscape plants such as shrubs, trees, and ornamentals, and they are also good for perennials for winter protection.

However, there really is no advantage to mulching them into the lawn. Be aware that if they are mulched and applied too thickly, it could cause decline of the lawn by smothering it. The breakdown process of pine needles is quite slow so it would provide a minimal amount of value to the lawn and the soil. Pine needles have a slightly higher carbon-to-nitrogen ratio than deciduous leaves, but they have a chemical component which makes them more resistant to decomposition. Pine needles also contain a waxy compound that makes then slow to breakdown.

Here are a couple of articles about the benefits of mulching deciduous leaves into the lawn:

http://csuhort.blogspot.com/2014/10/ugh-dealing-with-leaves-in-fall.html

http://csuhort.blogspot.com/search?q=mulch+leaves