Hello & welcome, I am Dr. B, a licensed veterinarian and I would like to help you today. I do apologize that your question was not answered before. Different experts come online at various times; I just came online, read about your situation, and wanted to help.
Again I do apologize that my colleagues could not aid you sooner. If you would still like assistance, can you tell me:
How long have they been scratching their faces?
Have you been using any new products at home (ie carpet powder, laundry soap, etc)? Any new plants they may have had access to?
What flea treatment do you use? When did you last apply it?
Photos would be lovely if you can post those for me. To do so, you can use the paperclip icon on the tool bar above your text box. Or if you can't see that on your computer/phone, then you can post them on any other site (ie Flickr,Photobucket, imgur, etc) and paste the web link here for me to check.
What dose of Benadryl are you using? How much do the dogs weigh? How often are you giving it?