I agree with Barbara, you are doing all you can for your nephew and i respect you for that. I think the important thing here is your concsience which should be crystal clear. It did my head in also when my xab family would call me for advice, it gets so tiering in the end all i would say is "Ive done all i can, if you can think of anything else that would be brilliant". I think people in general would rather someone else sort out problems and in this case they have nominated you, but it is not all your responsibility, please remember that.
take good care of you
Mair xx