A really serious question?

my mom has had 13 pregnancys... she only kept two of her kids (me and my lil sister) and she also had a couple of miscarriges....i have four brothers and two sisters i have never met my mom wants to search for them...not to talk to them unless they already know but just to make sure there alive....its been my lifelong dream to find out about them and were just not sure where to start ... how do we go abut finding out any information on them we know only there birth names(witch seem to have been changed) and there date of birth ....i have been trying for months to find them .... any help??