not sure what happened

i may have two half sisters who were possibly adopted. i know the parents names well i know their mothers first name, i know that the state of new york was somehow involved with the removal of the children. i do not know there names no one will tell me anything except that it's the past, i would like to at least let them know that someone cares. they would be at least 48 (the youngest) as of 2003, and i have also been told that they have another brother who is older than me but supposedly the youngest but also supposedly by a different dad. is there any way of finding a link without irritating my parents who seem to think that it's to late to have a relationship with the children with the little bit of info i have?