I would tell him to talk to his childrens doctors office and see if they have a social worker he can talk too. I ended up not getting disability until I was over 18 but when I did apply the social worker at the hospital/drs office is the one who helped me get everything started.
If he has already applied for disability for his kids I would ask the social worker how to go about filing an appeal. I filed an appeal on my own when I was denied the first time - the appeal went through without a problem and I was approved. The whole process - from my first application through my appeal and when I was approved and received the first check was almost a yr.
A social worker could definitely help though - if they can't help they could probably put you in touch with someone who can.
Also he could talk to someone with the CF Foundation. I knowin Florida there is a thing called CF Abilities and it requires an application and drs evaluation, but it is basically a program that once you are approved it helps CF patients pay for things like some meds that aren't covered, gym memberships to maintain health, I have even heard of it covering air filters for cars and things like that. Maybe the local chapter of the CF Foundation would know if there is something like that where they live - I know I heard about it through our CF Foundation Chapter in town.
Hope you find help soon,
Lindsey