I certainly would discuss it all with the 19yo openly and honestly. You might be surprised at how much he already is aware of. Your 13 yo also needs to know but not on the same level as the older one. Age appropriate information is what she needs.
I strongly suggest individual therapy sessions for both. Divorce is always difficult for kids regardless fo the reasons. In this case both have already learned unhealthy behaviors and need help understanding what is unhealthy and what is not going forward.
As for you and ACOA, take a look at the ACOA forum and read a bit. I certainly don't see you and your siblings all marrying alcoholics as a coincidence.