How to find my boyfriend's birth parents?

yah, I fully understand and can see it from their view, thats why I don’t want to meet them or get involved in any way in their life. we do want to see photos of any siblings and of his parents though. and see medical history. in fact we don’t have to know names, we just want photos!! only because we are curious. And if his parents are successful, something prompts me that they would be so proud of him. he is the best person I know. he is superman with a heart and mind of gold. He is a very smart man, he does very well for himself and is very smart with life stuff like financials and decision making. I love him very much and trust my life with him completely. I jusy feel they would be proud and wish they could partake in such a wonderful person. they are missing out. yet I would hate to be disapointed, what if they are a bunch of ungrateful grumpy pesimists? that would be terrible. so yah…hard decision. I guess the whole thing that has motivated me to search is my sister inlaw had two kids when she married my brother. then he adopted them because their dad was a dead beat. my brother and my sister inlaw had 4 kids together. about 4 years ago my sister inlaw shared with me that she had another son when she was really young. her parents forced her to I’ve him up when she wanted so badly to keep her baby. everyday she thought about him. she cried a lot wondering how much he look like her other two that were also born from the same father. She decided to search. she found him and they recently reunited. he came to stay and met our family. it was amayzing. I saw this light in my sister in law ever since. its like her life was missing that link and now its complete. I just wonder if my honeys situation was at all like that or if his parents even feel anything at all. I am saddend over it knowing that possibly his mom thinks about what he is like too. My man even told me once that he has a inside feeling that he was abandond. we understand why they chose adoption, but I wonder if his parents were forced to make that same chioce or if it was completely their own. lots of things to think about huh. just sometimes it really gets to me. I wish I had some answers.