Hi , I am sorry to hear about your Dads current situation.
Whilst we are all different I hope to reassure you in two counts. My cancer has spread to my lymphs around my body but not to my bones.t4n1m1a PSA on diagnosis 342.
I had docetaxl chemo and had few real side effects , I was never sick and only felt ill for a couple of day so over the whole 18 week cycle. I still ran and got out so please don't dismiss it as something that will spoil your dads quality of life as it may not.
I am currently on abirarterone, and have been on it for 12 months, it reduced my PSA to 0.17 and has stayed there for the last two tests. I have had little side effects from this too, perhaps slightly achey muscles/joints but I say perhaps as it may be the running I am still doing ( I am running a 66 mile race this weekend so these things can work!).
As I said at the start everyone is different, I do not see a downside of having a go with docetaxl as if your dad tolerates it like I did it will not affect him much and extend his time, he can always stop after the first cycle. After that go for Abirateone if that's what the docs are offering as again it may work well.
Hope this helps.
Kev