Adoptee Question

My (US) wife (Canada) and I are filing for spousal sponsorship. I am an adoptee. I was born in the US and adopted in the US. My biological mother has other children. Only one was adopted into my adoptive family. The others were adopted into other unrelated families in different states. Do I have to list the ones who were not adopted with me on my application? I do not have contact information for them which is a field on the application. If I have to list them for genetic reasons how do I inform immigration that I do not know of any way to contact them? Any and all help greatly appreciated!