You should have blocked them absolutely everywhere years ago so do it NOW! The less you know about them, the less they can cause you stress. There's nothing that you can do or say that will ever change who or what they are so stop trying. 

What they're doing with the texts and messages can probably get you a restraining order against them. Consult a lawyer to see what else can be done - their smear campaigns are designed to cause pain and are a tissue of lies. Sue their arses off and hang them out to dry.

Sounds like social media is a big part of this.  I would probably go into your settings.. and block them on everything.. or.. delete social media period... maybe set up a "fake" profile to quietly see other people's stuff.  

People write narratives in their head.. trying to blame others for their situation.. little you can do but ignore.

Spend your energy on people "in person".. that you know and cherish.

You have to block them. The only reason they do it is because they know you're watching. And you reading it isn't helping with your mental health or maintaining peace.

I have a mentally ill Aunt. She has bipolar disorder but claims she was misdiagnosed. My grandparents gave her the world growing up. After she was well into adulthood, they cut her off financially, the narrative changed. She started a smear campaign on FB about how abusive they were, how they did nothing for her, etc. At one point, she even accused my Grandpa of sexual assault to try to extort money. It had to go through court proceedings and everything only to be unfounded (which we all knew). We cut all contact with her. It's been almost 20 years and she is still smearing us all across FB. She lives in 100% victim mentality. The difference is, we all have her blocked everywhere, so we don't know about it. We only know when we hear about it from others. 

Think about how sad and pathetic it is for skids to live in a lie for the rest of their lives and that they have nothing better to do than spread it on FB. Block them, cut ties, and move on, thoroughly enjoying your life. 

Please, for your husband's health, block them. Really, if they get mad that you block them how much worse could they act? 

Sometimes you just have to close that door. 

Hit those shitty people where it hurts.Block them. Trust me they love to hurt you.

Blessings

ETA change your user name flip the script hun. "They are nothing to me"

Instantly that takes your power back.

Its time to heal

For much less, I have blocked my skids from seeing anything of mine on social media and I do not have their crap in my feeds. I have pretty much ZERO contact with them via phone--text or calls--again, for much less than the chaos, drama, and abuse you describe. Like others have said, block them. You don't need to offer an explanation. Just do it. The peace you will feel will be amazing! 

Block them on all social media, phones, any devices, and smoke signals.  If you can get a restraining order, then do it.  If there is ANY legal action you can take, take it.  You and your husband do not need this with his bad heart.  Your kids should block them too if they will.  If your kids choose to be in contact with them, they need some hard boundaries.  Your names should not even be mentioned in skids company.  

Let peace reign in your house. These folks have created, bought and sold their own narrative to themselves. I was also so very very good as a stepparent and tehy have a very different narrative that they told themselves so many times that they now believe. I use to combat the lies with facts - but it fell on deaf ears. It's time for you to focus on YOU and for your husband to focus on his health and for you two to put you two as the priority. This doesn't sound like it will ever be healthy but you can be healthy, that's the only power you have. 

I continue to strengthen my social media settings - so I don't see anything they post and after a big cry fest this year over my very HAPPY social media content I have limited their ability to see what I write. This is 100% what you should do.

For your husbands sake and your sake, block them on social media. Dont read those texts except to gather info for a restraining order. Get your wills and trust docs in order also. All the legal and financials possible.

YOUR bios absolutely need to hear the truth - give it to them full force. They are drinking the kool aide because they think once you and DH are gone, thats they family. Ive seen it and lived it.

SD25 Feral Forger sais the same thing to HER father. "You abandoned me, you left me for theat wh@re of a wife, you are just the sperm donor good for money and not much else." He still helped her - moved her twice from 300 miles away and gave her $400 dollars. This was before the wh@re of a wife comment...now after the latest money grab attempt, shes blocked the family and him and gone radio silent.

Your husband does not benefit from reading those texts. He must block them.

I am sorry you have terrible adult skids too.

Mine are passive aggressive, not outright hateful. It's not much better though. DH still hurts.

They've rewritten history and believe their own lies. You can't combat that. Agree that blocking them will help with peace at your house. 
 

I hope it helps out newly Sp.   that if SK start to disrespect you. It will continue for the rest of time.   So don't let disrespectful SK control your life.  Your bio kids gave up things for what ?   To have theee mother bad mouth by SK 

I think I have PTSD from having adult step kids, and step grandchildren
 

Shit I did too when I was living with a delusional entitled Disneyland dad, dealing with his conniving breeder, and equally conniving bratty clingy needy children every weekend every holiday. 
 

I drove 200 miles one way to get them each weekend, then my husband and I would take them home on Sunday

You a good one. I hope he compensated you VERY well

for this. 
 

What can we do? 

Aside from staying active in grand kids lives to prove them wrong not much. They will reap what they sow eventually 

Second the PTSD.  I hear ya. 

Echoing the others -- block them and be done with them.  Takers wanna take.  You sadly can't make people care at the end of the day.  You sound like you did an excellent job with what you were handed, and they ought to be ashamed of themselves.  Lots of people aren't happy with the decisions THEY made in life, nor happy with themselves, so they look for scapegoats left and right, rather than change literally anything about themselves or the situation.  Let them be victims.  Own your truth.  You know how much you cared, tried, attempted.  They are hurting and impacting your health, don't let them waste another second of your wonderful lives worrying about them, as much as possible.