If they are dying then the infestation (if there is one) would be readily diagnosable. There will be D-shaped exit holes in the trunks. Also if you where to remove a section of bark you would find galleries made by the larvae. Confirm that EAB is the cause first, then yes, removal of infested trees would be recommended. Google Emerald Ash Borer, head to the site to get pictures of the damage/exit holes. With a plot that size, if there is EAB you're going to be in an up hill battle to save those Ash, sorry.