Hi, I was wondering, if two disciples were at one time being taught by one shifu/shizun (i.e., they were shidi and shixiong), if they were both kicked out of the sect, would they still be able to refer to each other as shidi and shixiong or would it have to change to ge/di or just using their formal names since they aren't technically under the same teacher anymore. For context, the two disciples don't get along very well. Also, separate question, but can a disciple have to shifus at once?
It depends on whether or not you decide to follow Chinese Culture Norms or not. As I don't know Chinese Culture Norms, let alone the ones those terms of address are based on, I don't actually know the answer for certain. However, I would assume that the decision can be made on an individual basis in those situations. In this case, I would assume that, should they decide to stay together for one reason or another, the "senior" disciple would prefer to keep the terms, while the "junior" disciple would be happier abandoning them. This is because I believe that terms like those are used simultaneously as a notation of polite respect and acknowledgement of one's experience. That is to say, you call a person of equivalent "rank" but more "experience" the local "senior co-worker" equivalent out of manners and with the underlying implication that if you get into trouble with something about your work, you can go to them for assistance, same with them calling you the local "junior co-worker". Even if you don't like each other, and they're the last person you'll be willing to go to for assistance, even at work, there is still that implicit social contract in those terms. That is to say, the "senior" would want to keep using the terms, as it allows them to retain some symbol of authority over the "junior", while the "junior" would rather abandon it due to the fact that the implied relationship is no longer existing. But, and I can't stress this enough, I don't actually know the rules of Chinese Culture that would determine this, so I can't actually give an answer that can be said to be 100% true. This is merely my guesses from reading stories written by Asian Authors, as well as my interpretations of what the terms used both mean and are used for.
In Chinese culture, people close to one another have a large range of ways of referring to one another. In this case, the form of address has more to do with how they think of to one another rather than what school they belong to. So for example, you can have two characters who have not seen each other in decades, and who were never formally in the same school, but still refer to each other with these terms because that's what they feel comfortable with. Do note though, that it's rare for a senior student to refer to someone as "shidi" unless they're unfamiliar with each other. It's just one of those quirks of Chinese where the older person will generally use a proper name rather than a relationship term. Absolutely. The general conceit in wuxia and related stories is that the student is supposed to get the permission of all of his current teachers before following another one. In the real world, this rule was more relaxed, and it was quite common for a rich person to have multiple teachers (usually different ones for different sets of skills).