That would make me go nuclear!

Jesus. Idk. Even if it's just emotional incest with borderline creepiness, gtf out if there. Gross! 

Also, if all involved are adults, i don't think there is anything an attorney could do. If they wanted to have 2 sets of little web-footed kids together, that's on them i think. Just leave them to their grossness.

ETA not meaning to insult those with birth defects. But you can't stop these adults from having sex or whatever it is they are doing. Just leave!

I applaud that you are not tolerating this crap and are getting things in place to bare his pervert ass as you get on with your life.

Don't wait too long.  Rather than baring his ass in front of a counselor, I would do it in front of a Judge with all of his kids in the gallery.   Or better yet, have him bring his checkbook and the deed to your house to sign over everything or... it will be made public record in front of the Judge.  Keep copies to send to his kids after it is all settled.  Send copies to his parents and BM too.  No need letting him off with just a divorce.

I had to do something similar with my XW when she backed out of the settlement she proposed and we both had agreed to.  She proposed a single lawyer uncontested divorce and she presented the asset settlement which I agreed to.  She wanted the CD she had cashed when we closed on the home we had purchased three months before she moved out and informed me she wanted a divorce.  I agreed to her proposed settlement, Closed out joint accounts, had the bank cut her a cashier's check and moved all of our cash to new accounts in my name only.  Over the next couple of months she got squirrelly as hell and engaged her mother's business attorney to refloat the agreement she had formulated.  So.... I met with she and her new attorney with notarized copies of every paper I had written for her during her last three years of college, I had written them all, the drafts in my hand writing and the final typed graded copies, notarized copies of every page in her several year long multiple volume diary with specifics on her many lovers including names, dates, hotels, etc, etc, etc.... all in her handwriting. 

When I handed her attorney the manilla envelope with her notarized academic fraud and  notarized copies of her adulteress history during our entire engagement and marriage my XW about stroked out.  Her attorney reviewed all of what I provided, informed my DW that he could no longer represent her. He was an Adjunct Prof in the law school of the University my XW got her BSN from.  Or more accurately, the BSN that I wrote every paper for.  Her attorney told her he could not inform the university of her academic fraud due to attorney client privilege but neither could he continue to represent her.

She came belligerently back in alignment with her originally proposed settlement and the single attorney uncontested divorce. She did get lippy with the Judge during the divorce hearing which cost her any share in the home so all in all I got out of that marriage in about as good a position as I could possible have exited.  Most critically, I did not pollute my gene pool with that skank whore.

So, take no prisoners, go for total domination and make it clear that they never want to have anything to do with you again.  Three years post divorce, my XW did try one more run at me but... that cost her, or more specifically, her geriatric Fortune 500 Executive sugar/baby daddy cheat partner five figures and a half when she decided she wanted my house/the house she and I had bought a few months before she left to hang out with grandpa sugar baby daddy.  

Go for blood!