I believe fellow TAs are giving students answers and inflating their tutorial average, what should I do?
Is it possible that the other TAs, by having done the course before, have a better overview of the kind of questions asked in the exam (based on those of previous years), and therefore are better able to train students for those exams? That would explain the facts as well, without anybody consciously in the wrong (and it is always worth to explore such possibilities).

I can also understand that your professor is not actively doing anything about it as long as the difference is not too big. Some TAs are better than others, some groups are better than others, there is always noise and some differences between groups are to be expected. I was a TA for several math courses where we would grade weekly assignments of our own groups (that counted for 10% of the final grade, next to a 90% final exam). I would grade harsher than other TAs and my group's average of the homework would be lower than that of other groups. However, my group tended to do better at the final exam, I believe in part because they were pushed harder to make an effort. What I mean to say is that worse intermediate test results don't say everything.

Unless you have hard evidence that your fellow TAs are 'gaming the system' I would be hesitant to attach too much meaning to the present facts. If, besides this, their manners are unpleasant or the group atmosphere isn't right, the easiest solution would definitely be to avoid them by not TAing the same course next year.