Definite articles are not used when referring to a single family member, e.g. mio fratello, mia zia, etc. However, it is necessary to use an article when referring to more than one family member, e.g. le mie sorelle, i miei fratelli, etc.
I actually typed tio instead of zio and it was accepted (and not because it thought I had a "typo in my answer." I, too, have trouble understanding the male speaker. Plus, he speaks very fast and I usually have to click on the slow-down option with him.