You can give benadryl and I will direct you to site with dosing and information. Of course any over the counter drugs should be discussed with your vet, especially if the dogs are taking any other medications. http://www.petplace.com/drug-library/diphenhydramine-benadryl/page1.aspx
You can also give over the counter melatonin, found in any drug or health food store. Here is more on this.
Turn the tv or radio up high to lessen the noise of the firecrackers.