This one is really hard because even though you understand and your husband understands that they care so much, they have their own feelings, which then creates more pain and stress in you. I remember feeling like breaking down to my sister one day just saying, your feelings of love and protection to me are creating more stress within me than our situation together. What I would recommend, I don’t know what your situation is, if you and your husband are working with a therapist or you’re not, or he’s working recovery or not, or if he’s angry with you for disclosing to them, which I’m grateful that you disclosed too, that you had some support.
What I would recommend; First, if you are working with a therapist, there is actually a restitution exercise that we as therapists use for this very situation to help put into words the way that their, the addict, their actions have impacted family members. And really, your mom and your brother, all they want to know is that he really understands the pain he’s put you through.
So to just finish up answering your question, I don’t know if he is in the place to be able to write such a letter with the therapist if he’s working recovery, that’s something, if therapists would want him to do an emotional restitution of family members. If this is really just about you and your relationship with your mom and your brother, I would have you write a letter, I would encourage you to write a letter explaining how grateful you are that they have been there for you and that they have given you support, and you know how much they love you but how much stress it causes for you to feel anxious about their feelings toward your husband, and to be able to just communicate that because they love you, they want the best for you, if they know that their protective nature is causing distress, they will likely change, if you use your voice communicating that to them.