Whatever avenue you take be sure it is one that will hopefully minimize the problem. We like the idea of stroking instead of poking, at least in the beginning.
Look for the opportunity to talk with them and share their concern....take ownership, even if there is none to assume. Tell them you hope they have been seeing an improvement and that you are trying really hard to keep their concerns in mind. Being positive, showing support for them, and owning the problem may make a difference.
It may help to provide them with your cell number and tell them to call you whenever the hear the dogs acting up. Let them know you really don't want them to be unhappy with you as a neighbor.
NOTE: they do sale no bark collars in pet stores just a suggestion
I would speak to your attorney and he will be able to guide you but I was in a very similar position recently and a letter from my lawyer telling them to leave me alone was enough to keep them permanently off my back.