I'm a regular who has name changed due to the sensitive nature of this post..
MIL is a complicated character who I have grown to love. DH has a half sister who he was brought up with, MIL told me after a few drinks that the man SIL thought was her Father in fact is not, her Father is a man MIL knew when she was 19. She asked me to look this man up, I was hesitant at first due to the potential consequences but after a couple of years agreed to find him (she's not internet savvy). She didn't mention the fact he was SIL's Father again, I'm not sure she remembers telling me. I have seen a photo of him though and he is her doppelganger. The man she thinks is her Father didn't even make contact until she was 15 but from what I gather they are close now..
I found him and wrote him a personal letter explaining my MIL (who he knew 40 years ago) would like to make contact, as a friend. His wife called me, she was shocked to receive the letter but would give him my number. He called the next day to say he was also shocked and does not want contact with MIL.
MIL is eagerly waiting his response, I feel terrible adding to the amount of rejections she has received throughout her life so wonder whether it would be better to tell her I didnb't receive a reply? Would that BU?