Lori67, congratulations on your new marriage. Things do sound tricky for you at home though.
In order to gain some improvement in the relationships with the children, have you really tried being careful and ever so kind your husband’s children? You do sound a caring sort. Can you give the same kindness you’d give your own child, and then do a bit extra?
Small kindnesses can speak volumes. Perhaps buy them some shower gel they’d like, smile gently when you encounter them, leave them a note saying “Saw this, thought you’d like it. x” So it relentlessly, even if they do not acknowledge any of it.
Undoubtedly these young adults are hurt. Yjey are still young and might not approve of their father and believe they owe you no courtesy because you and dad have trampled on their feelings.
You could think of them as being vulnerable to the slightest offence, like a burn victim would fear every touch, even if kindly done. And only engage with them very very gently.
In order for your marriage to be harmonious I think you are going to need to put in 100% TLC and to do it, without it being recognised, for a long time. It’s going to be an uphill struggle. It will require a mindset change on your part. If they are hurting as much as I imagine, then you might want to treat them as if they are completely vulnerable, and do absolutely everything possible to make them trust you and believe you are definitely loyal and kind and prepared to fight their corner.
They will have mixed feelings and will be unlikely to be totally negative. I hope you are prepared to be humble and prepared for the slog. Not that you should let them wipe their feet on you. It’s a tricky balance but your aim is to earn their respect. They needn’t like you but it would be great if you achieve respect.