Austrian Pine Diessed
Sadly Austrian pines are susceptible to Dothistroma needle blight. I’m attaching a MSU Extension bulletin about the needle blight.
If you believe that the trees cannot be treated and need to be removed. The timing could depend on their location since they are so large and heavy equipment may be needed. I suggest that you consult a certified arborist for professional help. Go to www.treesaregood.org, the website of the International Society of Arboriculture to find an arborist in your area.