Those expressions all mean the same thing, but I'd say there's enough of a difference that I wouldn't say they're interchangeable. "Over the course of" and "in the course of" are both interchangeable. You'd use this together with an amount of time, or an event. For example: "Over the course of a few years, they learned many things about themselves." You can use "Over", "In", or "During" pretty interchangeably here. You could also say "He fell asleep three times in the course of the meeting yesterday." Again, you could use over/in/during. "In the process of" is a little different: here, you don't really use this with time, you use this with an occurrence or action, or something happening. For example: "In the process of finding her keys, she also found some coins behind the couch." Here, we're talking about something else happening at the same time, WHILE she was finding her keys. It feels somewhat unnatural to use "In the course of" and "over the course of" in this case, since the act of looking for keys isn't really a period of time. As a rule of thumb, "over the course of" and "In the course of" take nouns, periods of time, etc., while "In the process of" takes a verb in the progressive tense (asking, doing, finding, etc). Hopefully this helps.