I can't see having letters from a doctor and the school is going to really help. For example the school can't force them to come back, only you can. Being notarised is fairly meaningless - it doesn't make the contents any truer.
There is always a chance they will be granted with a visit visa and the only way to find out is to apply. Obviously there is a chance the visas will be refused and the fees wasted.
...I see
Thanks for the reply Darren, will have to think of it..