Where the breathaliser may be useful for satisfying your knowledge that your wife isn't drinking at that particular moment, it won't alter the fact that if she wants to she can get a negative reading and then go for the whole box and bottle once you are out of range. Whilst she is out for example. I think it also keeps your focus on your AW, feeds your obsession with her drinking. To me it is just another version of counting empties. (Oh how I know this futile act of counting bottles). It serves no purpose whatsoever, except to wreck your day, and perhaps give your AW the amunition to accuse you of trying to control her behaviour, which of course, you are. We all have and do, but we are learning not to one day at a time.
Houston I don't have any idea how you are going to stop your AW driving when ever she wants to with or without the children in the car. But I suspect that in the US, as in Aust there are child protection laws within family law that can at the very least become court orders. Enforcing those laws is another matter entirely. Even if you separate there is every chance that your AW will have joint custody. If her disease remains untreated she will continue to drive under the influence of alcohol with and without the children in the car.
You are going to see a Lawyer so that is the first step in using the law to protect your children. But IMHO a step toward the doors of Al-anon may give you the support needed to deal with all of this yourself, and that will ultimately be of major benefit to your girls.