You could try some general adoption books, too. Maybe
Twenty Things Adopted Kids Wish Their Adoptive Parents Knew and tell your family the reason you are doing open adoption is so our child will have answers to a lot of these questions growing up. Also
Adoption is a Family Affair is an okay book that pretty much tells family members to cool their jets with the unsolicited opinions.
Talking on the phone and sending letters and pictures is also pretty common (even in closed or semi-open adoptions). You haven’t had a post-placement visit? You might tell them that some people visit monthly (we do this in our OA), some people even go on vacations together and such, so really what you’re doing right now is pretty moderate compared to some open relationships (I’m not trying to diminish your OA, but I found the “all the other a-parents are doing it” argument to work with my family. Maybe there’s strength in numbers? You could also tell them about other families you know of that are in successful open adoptions).
Our family got to meet our DD’s birthmom at her baptism recently and I think that kind of calmed their unfounded fears about her (Was she crazy? Would she try to steal DD back?). Is there an occasion where you could all get together (like a birthday party for your child or other special event?) and they could see that your child’s birthmom is really just a nice person who cares about your baby and doesn’t want to hurt any of you?
You could also assure your parents that the reason you chose open adoption was for your child. You have researched the issue, carefully weighed the options, and believe that it is in your child’s best interest to have continued contact with the birthfamily. You’re not doing this so that the birthmom or you feel good about yourselves; you’re doing this for your child, so your child can feel good about where he or she comes from. I have told my parents that if we believed that our DD was being hurt by it in any way we would cut off contact (which we would, but only if some major change occurred that truly was harmful to her).
I don’t think you should be embarrassed about the choices you’ve made, but I’ve found one way to get them more on board is to back off slightly and explain things in a lighter way. Such as, “we really only talk X times a month, which is pretty common in adoptions,” or “almost all adoptive parents send letters and pictures… and I like doing it because it’s helping me to create a special record of E’s life,” or “we’re open to doing visits, but E’s birthmom isn’t ready for that right now. We hope someday she will be because we want E to be able to meet her” or “E will have access to a lot of information about her medical background and family history because of our continued contact.” I also think that saying, “E’s birthmom chose us because we are willing to be open” is a good idea because it emphasizes to them that they might not have this beautiful grandchild if you had been more closed.
I think it is harder for older people and they may never understand. But if you keep things about your child, hopefully they will see the benefits of the open relationship and back off over time. At least I hope this is the case. My DD is only 3 months old, but I’ve found people have eased their opposition as we talked about OA more casually and kind of framed things in a this-benefits-our-daughter and its-really-not-that-big-of-a-deal sort of way…