I'm in a somewhat similar situation, and had a lapse in contact with my daughter's a-family after an adoption that was originally open. Just a few months ago, I decided to contact her a-parents in hopes to reopen the adoption. (She is 14, and just started high school), and her a-mom seemed very happy to hear from me. She also said that she would tell her "soon", probably because of everything going on in her life as well. I haven't heard anything from them in a couple of months, but I did send a letter a few days ago for my daughter, which the a-mom thought was a good idea. I would assume that she would tell me if she told her about my letter , so I don't know if she knows. But I feel the same way you do, I don't want to disrupt anyone's life. I told the a-mom in the letter that I wanted to reconnect with her, and eventually bring DD in to it when she is ready. I told her that I trust her judgement as to when she feels the time is right to tell her. It is going slowly, but I think that is a good thing, because at least from my end some wounds left over from the past resurfaced unexpectedly, so it's given me time to adjust to that and the possibility that I may someday have contact with my daughter.
I would definitely try to keep in contact with both of them, maybe letters and pics with the a-parents, while they try to sort out what's best between the two of them. I'm sure once they get reaquainted with you, they'll so much appreciate your patience and the respect of letting them handle the situation the way they feel appropriate. I would also be honest with them, and let them know that you'll respect whatever decision they come to, so that the lines of communication are always open for everyone to share honestly. At least now you know that when your daughter is ready, her family knows where you are, and will be supportive in your reunion!
For me, the day I got pics, I was SOOO happy!! Cherish eveything you get! Good luck!!