You do know what to do - protect your DS. In this situation, your biological children must be your priority, you are their mother & it's up to you & you alone. I'm not sure how how old your DD is but your DS is defenseless & the thought that your are putting your (severely messed up) SK's needs before his makes me angry on his behalf. You must be a very lovely person, to be trying so hard to fix the (in my opinion) unfixable SK's, I give you credit for that but in this particular scenario, anything other than getting your kids out of this situation is just background noise. I hope others can give you more practical advice but mine is simply to save your son. I'm sorry you & yours are going thrpoug this. 

You need to act NOW to protect your son - are you going to wait until your SS kills him before you act - which might not be that long, judging by what he has done already?  Due to his work, your DH is not around to parent his out of control children, and you should not have charge of them in his absence.  Neither of these kids' bio parents is behaving as they should, and you should not have to pick up the slack.   You really need to get out of there with your son and daughter, immediately.  Do you have relatives you can go to?    You seem to have been put into a helpless and paralysed state by the chaos going on around you - but you need to take charge of the situation, like now! 

You know exactly what you have to do. Protect YOUR child. Your husband has a responsibility to all the kids but if he isn't home to parent these kids, then they can go back to a boarding school for kids with behavioral issues, back to BM or to another relative. It isn't your concern where they go but they need to GO.

It is likely that BM is just going to be awarded weekend visitation due to the history. Once that happens this behavior is just going to escalate. Get your children out of that situation. I am attaching a link to one school that I know of that does scholarships and grants. My IT person sends her 2 kids with behavior/mental health issues there. She said it changed her and her kids lives. She only pays for transportation costs. It is called "boys ranch" but it is for boys and girls. It is a therapeutic school.

https://www.calfarley.org/boysranch/

Remove yourself and your 2 children until ss receives some serious treatment and things change     They seem to need counseling with what they have going on and maybe even an inpatient stay at a mental health facility if things keep going the way they do with ss. But don't leave your poor kids in his way. You don't deserve to be stuck there with them either. Put your 2 first with this situation,  it can get dangerous. I always consider my step daughters needs and wants but when they have something going on that negatively effects my BDs, that's when their needs take a back seat for me. 

I know this is super tough.. especially with your husband's job.  my DH worked offshore as well.. and it is difficult because they make really good money.. but it does mean that the burden for shoreside falls more heavily on the spouse or family.  NOt sure what is occupation is.. but I do understand that  his skills might not be usable on dry land.

But.. there is no way his kids should be abusing other kids in your home.  These kids MUST be in therapy.. and there MUST be high supervision especially for your 2 yo.. you just will have to be vigalent.. or get help so that there are more sets of eyes in charge.

He has to be home every night.  He made those kids, he has to take care of them.  Oldes SS is sick and should be in a residential treatment place.  You must protect your kids.  If you have to move. Move. Then your DH has to parent his kids or they go into the Forster system that his choice 

The skids say they want to go live with mom. BM, if she's taking your DH to court, must want them back. Would the court allow them to go back? Has BM cleaned up her act? If so, let her have them. If your DH isn't there parenting, and your bio is in danger, these skids should not be in your home.

Protect your bio first that is your obligation as a parent.

Next...I need to address BM's claim that she was strong armed into current custody plan.

She is a drug addict...expect nothing less ok? She needs money.  Kids are young,,,i doubt if she can brainwash them to her side. Give it a few more years then she will go back to court again. ------------

Back to my point:

She would not have had a choice in the matter---kids were removed by cps..it became a court matter as you well know. BUT BUT BUT....ma'am, IF she 'signed over all legal rights"..then she would have Terminated her Parental Rights... and have zero visitation.

 I believe what you do mean is mom was formally charged.. the charges stuck,  then felony convictions resulted in her loosing custody via family court. Is it fair to assume she has Felony Child charges on her record now.

By the way---lets hope she has sup visits at best. For mom to ghost for so long, I am shocked her rights were not formally terminated.

GoodLuck

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(2 whom ate adults) ever dared tk lay a finger on my kids, hubby would be made to remove them from our hone and presence and i would be reporting to the police.

skid is beating your child up to cause serious damage and you’re more worried about keeping the peace. 

That cannot happen as long as ss is allowed to hurt your child

Time for the cops to haul this violent little shit off to jail for his violence towards your toddler.  The next time he attacks you or your toddler mace his ass and hog tie him (for his own protection) until the police come to haul him off again.

Lather, rinse, repeat.

BM abandoned them.  She is the cause of all of this.