I know that you use と for complete lists, and や for incomplete ones, but when would you use xもyも instead of xとy or xやy? Doesn't も usually replace は or が? Why is も used for lists at all?
More detailed answer:
I'll start by stealing one of my examples from whats the difference between し and と?
This example clearly states that I'm buying 3 things: apples, carrots, and peppers. If we change と to や, however, we get:
Here we're probably buying more things, but the only ones we decide to list for the listener are the above-mentioned apples, carrots, and peppers. The full list may very well be too exhaustive to list everything out in conversation.
As for も, It's not used so much for creating lists as for expanding them. For example, it wouldn't be inappropriate to follow either of the above with:
...indicating that I need to buy rice as well. I could even list a couple of items in this case:
Now that said, so far we've dealt with lists of objects. When it comes to lists of people, my observations are a little bit different:
is a perfectly acceptable construction. It's just like substituting "with" for "and" in such a list in English, and presents a slightly softer nuance.