student transfer to green card

Hello,

I have relatives who have already applied to immigrate their family
to the U.S. They are currently on the waiting list to get their
visas. They have a 11 year old child who is already in the U.S. on a
F1 student visa. This child is also on the application for the whole
family. Will this have any affect on the family's application to
immigrate? Also, when it is time for the family to be interviewed,
does the child need to return to their country to participate? Or
is it possible for the child to be interviewed in the U.S.?

Thank you.