I will answer your questions. First I suggest you watch the video webinar by Dr. Michael O'Donnel of University of Iowa. The webinar was presented in 2013 but it covers the whole aspect of the treatment for non-invasive-bladder cancer, including BCG treatment. It answers many questions you have. The other one is the paper published in 2015 by several experts on BCG treatment. The author includes Dr. Lamm, Dr. O'Dommel. Dr. Kamat and others who are not clinical doctors but also have been involved in researches.
Webinar
Consensus statement on best practice management regarding the use of intravesical immunotherapy with BCG for bladder cancer
www.nature.com/articles/nrurol.2015.58
It is noted that Dr. O'Donnel had been using 6 weeks induction, then another 6 weeks, then maintenance in his 2013 webinar, but the expert consensus statement in which he was one of co-authors says the best practice is 6 weeks induction, then 3 weeks maintenance + subsequent maintenance. So, 6 weeks + another 6 weeks + maintenance had been used in the past, but now 6 weeks + 3 weeks (1st maintenance) + other maintenances. is what the experts recommend. This answers your first question.
I think it is good that you had paused after the 2nd treatment to avoid severe side effects, Dr. O'Donnel expresses his concerns in Q&A that some urologists try to push it through with more BCG treatment even seeing significant side effects.
In terms of 25ml saline vs 50 ml, I am only stating that 50 ml saline is specified in the product label of not only SII ONCO-BCG but also MERCK TICE ONCO-BCG and Japan BCG Tokyo strain BCG. I do not know how they ended up specifying 50ml in the first place. It is interesting to know the history of BCG treatment for bladder cancer. BCG treatment for bladder cancer was first established by a Canadian Urologist Dr. Morales in 1973. He tells that the reason he used 6 weeks of induction was that when he ordered BCG from the manufacturer of BCG for tuberculosis, it came in 6 vials. It just turned out that later study found out that 6 weeks of BCG treatment was the most effective.
You are doing great. I know you are trying very hard to cure your dad's bladder cancer with his bladder intact. That is good, and it is highly likely that your dad will keep the bladder. Also, don't be stressed out on a few hurdles you encounter for saving his bladder. I have known several people who chose and sometimes had to remove the bladder to save their lives. Dor most of them, the lifestyle has not changed from prior to the removal of the bladder. So, by a remote chance, that the removal of the bladder has become considered necessary, there will be some adjustment but overall his lifestyle should not change much. You take care of yourself too.
best