Hello Steffaffles and welcome to the site.
Yes Gleason 9 is serious but he is being treated so hold onto that thought.
Don't confuse the giving of chemo with worst case scenarios because as far as Prostate Cancer is concerned it is often given to enhance the treatment. It doesn't mean dad has been given it as a last resort.
There are many on here who will have the experience you need and I'm sure that now I've bumped you up the list they will be along to advise you.
If you go to Publications on this site there is the Toolkit which you can download and which is full of information which might be useful.
How can you help him? Well you're already doing that by supporting him and trying to find info for him. IT does help when he goes for appointments if somebody goes with him as there is such a lot to take in.
Try not to do general Google research as sometimes the stories are not relevant to your situation and it only produces fear.
If you have questions come back and ask them. Somebody is likely to know the answer. By the way, no question is considered as stupid or inappropriate if it is Prostate cancer related so ask away.
In the meantime, best wishes to you both
Sandra
*****