My parents are also toxic (and so we no longer have contact with them) so I can completely relate. The gaslighting (where they do something and then deny doing it, or go out of their way to hurt you and then tell you you have no right or reason to be hurt, or say something cruel and then tell you they were "just joking" or you should "lighten up", etc.), manipulation, and abuse are not going to go away. They won't change. They won't see reason. They won't start seeing you as a person with feelings and needs of your own. You're an object to them, something to play with and abuse at their whim. They want to control you. They don't understand (or refuse to understand) that you don't have to put up with it. It's up to you to show them. You're a grown woman and people don't get to treat you like garbage just because they donated your DNA. Family is supposed to treat you better
than strangers off the street. If someone you don't know from Adam started doing this, how would you react? What would you do to protect yourself? That's what you have to do now, to these people who have the audacity to call themselves your parents. I know it's easier said than done, and the first step is the hardest by far. But standing up for yourself will be good for you, for your marriage, and will serve as a fabulous example for your children, who see that Mommy loves herself enough not to let others trample her boundaries and feelings. They learn that no one gets to treat them like dirt, not even family. It's a powerful lesson.
I've been there, mama. It's no fun. Shaking up the family wolf pack hierarchy was the hardest thing I've ever done, but definitely one of the most rewarding. They don't live in my head anymore. I don't care what they think about me. I feel like an orphan, but that's better than feeling like an abuse victim and a bad person.
I agree with others that you should get Caller ID and stop answering the phone when they call. Or you can do what I did--make an all-purpose DO NOT ANSWER contact for your phones and put all their numbers in it, as well as telemarketers and other obnoxious people. That way when the phone rings and you see "DO NOT ANSWER" pop up, you can ignore it and go about your day. You don't know if it was your abusive parents or some guy trying to sell you a mortgage refinance, so there's a lot less guilt when you let it go to voicemail.
You can also make a throwaway email account at Gmail and have any email from your parents' email addresses forwarded there and automatically deleted from your main account's inbox. DH can check the throwaway account for you on occasion, but you don't have to see their letters or know how often they're trying to contact you. Best of all, Gmail archives everything forever, so if you need it for future legal purposes, it's all there.
You're very strong to stand up to these people. The pull of "But they're your parents!" is very very powerful and society frowns on those of us who were raised by abusers and choose to limit or break contact. That's okay; society doesn't live your life and isn't responsible for your and your children's safety. Let them frown.
Keep protecting yourself and your family. You're doing the right thing.