If he got in touch with Social Services they'd be able to make contact with the mother through the school... if he's comfortable going the official route. At least, it worked like that for someone I knew a few years ago. Not sure of your boyfriend's brother's situation though so it's just a suggestion.
I think he'd be very lucky to get the kind of info he's looking for off the net for free... and the fact that she's in Emmerdale could make it harder for him too, maybe.

Either way, I hope he manages to sort something out.