This is a nightmare, I'm so sorry to hear about your father's situation. The most important thing at this point is your father's comfort and it doesn't sound like they're doing very well. You should seriously consider hospice care, the help you'll get will be invaluable.
Is he on antibiotics?
What about radiation to shrink the bladder tumor or any tumor causing pain? I know that's mostly done for bone metastases in the US, but it's often used in Europe as treatment. If infection is present any treatment is likely to worsen things though.
It's true that the cause of death is often sepsis when bladder cancer gets out of control. Maybe he should be getting IV antibiotics?
How about pain meds, is he getting enough? It might be time for some serious pain control, there are many techniques for people in your father's condition. Hospice specializes in this.
There is information on the website about metastatic blc and end of life issues.
blcwebcafe.org/metatcc.asp
I send you my prayers and best wishes for your father's peace and comfort.
Wendy