Sorry to hear about your issues. Sort of "been there, done that" although not as severe.
First thing, you need to put yourself first. You are in a clinical trial and "they" may feel the need to maintain the prescribed protocol. You need to make some changes!! One thing, with the usual BCG infusions, it is not necessary to get the full dose. I was down to 1/3 by the time I finished the instillations, and it is possible to go down to 1/10th if necessary.
Second, if you feel that you REALLY do not want any more BCG that is your decision to make. From what you described you have received not only the induction phase but several maintenance treatments. You should have received most of the benefit of BCG and would probably do fine if you quit now.
If you are unable to complete the series in the research study, you are not a "failure" but have provided information that the researchers need to know.
Best to you
Sara Anne