Searching for my birth siblings born 6/24/57 and 7/15/59

I am searching for my birth brother and sister. My brother was born on 6/24/57 and my sister 7/15/56, and were given up for adoption by my mother. They were private adoptions facilitated by someone my mother knew and lost contact with. I have limited information other than their DOB's...the boy's name was Steven and the girl's name was Beverly...birth last name Van Dunk. Their names were probably changed and I do not know if they know they are adopted. They would have went to two separate families in the New York/New Jersey area, and I believe may have gone to a pastor in a church. My mother was recently diagnosed with breast cancer and this has been weighing heavily on her mind lately (which is why she decided to tell me) having kept the secret for over 50 years. I would like to do this for her and offer her peace and closure. She doesn't want to cause any pain or disrupt anyone's life. She just wants to make sure that they are ok and that they have lived happy fulfilling lives...something that she would not have been able to do at that time. Hope to find you soon.