It doesn't matter if they have an attorney.
the dogs were loose, and in your yard. You have the law on your side. Lawyers are good but they can only spin so much. Take pics of the fence that has been repaired many times, pics of the wounded chicken, a copy of the vet bill.
Add up your feed cost for the year and break it down to per bird. throw in your time, and potential egg value. Then pile on the emotional stress and loss of companionship.
They will not be able to talk their way out of it, or make it your fault their dog was in your yard. You will have them dead to rights. Then when you win, inform them that next time the dogs in your yard it will become fertalizer.
P.S
Stick to the numbers on all the tangible things you can put a dollar amount to.
Then with the emotional strees and loss of companionship make sure it doubles the amount your tangible amount is. If they have a good lawyer that cares about their interests, he will most likely advise them to settle out of court. Then you can say, well' I'll take half of what I am asking. Then your actual costs are covered.