Yes. This is a message that is absolutely typical of parents like this. There’s a whole website devoted to the things toxic parents say to their estranged children. They all look exactly like this. They will never accept that they had any part in you going NC, it will always be your fault!
I know it’s hard, but do not look for truth or meaning in messages like this. You know the truth. Don’t respond, ever. Dispose of the letter, get it out of your home. Burn it, cut it up and bury it, just make sure it’s gone from your life. A cremation or burial of the words can be very cathartic! Remember that they are his words and feelings, they are not statements of truth, and they are not your concern.
Your husband has betrayed you. In your shoes I’d hate to think of them chatting and laughing together when I was NC for good reasons. It would feel like he thinks they’re really not that bad.
It’s good to see that he and you have talked about this and you’ve found some peace, but I believe he’s profoundly wrong when he says it won’t do you any good if he and you don’t see them. He says you’ll feel guilty when they die. This is often said but is wrong. Many of us on here went nc or LC with parents and it did do us good, a lot of good, it removed their ability to hurt us and affect our lives and set us free, and allowed us to lead more normal lives.
Being in contact with them isn’t going to make you feel better or worse when they die. Imagine if you start seeing them again, they start on as usual, criticism, carping, complaining. They succeed in making you feel miserable again. Shortly afterwards one of them dies. How will you feel any better than if you were still NC? If still NC what exactly should you feel guilty about? Not letting them abuse you? Maybe that is how you’d feel, that you should have endured their treatment of you despite it not helping them or you in any way. But trust me, it’s likely that you’ll grieve (because they’re your parents), not miss them, get through the grief and be fine. The idea that you should allow yourself to be badly treated in case you feel bad when someone dies, is faulty thinking.