My mother-n-law retained an attorney for a divorce against my father-n-law back many years ago, they ended up remarrying and now father-n-law has passed away. The mother-n-law has his will with her being executer of the estate and she has hired this same attorney to represent the estate probate proceedings, isn't this a conflict of interest?

I don't see why it would be.

Because he would have been opposing counsel in the divorce against father-n-law and now he would be counsel for father-n-law's estate!

because he would have been opposing counsel in the divorce against father-n-law and now he would be counsel for father-n-law's estate!

No because this is a separate action estate / probate. It doesn't involve the 2 parties in conflict. This is a settlement issue.