Empyreans seems like a strange choice of name for children of the gods of any plane. It makes some sense when limited to children of celestial gods, but the word itself suggests origination in the realm of spiritual fire, which I would equate to the Positive Plane. Now, in my homebrew cosmology, all celestials, fey, and fiends, including "gods" of those planes, have their origin in the Positive Plane, so they would all be empyreans in that sense, as would those considered to be their "children" even though these are immortal beings who were "conceived" outside of the flow of time. For example, the archfey of the hunt, in some accounts, is considered to be the son of the archfey of crafts and his spouse, the archfey of living things. The three are coeval, however, and had these relationships from the beginning. Many mortals consider them to be gods.
Angels I would consider to be of a lesser order of the same type of being, so it makes sense for them to be a type of empyrean as far as I'm concerned.
ETA: Now, the question of how titans are involved is a bit of a mystery to me. In my homebrew, titans are the highest order of giants and are descended from primordials, who have a different origin from the "gods" described above, so I'm not sure how they became the children of the gods if that was indeed the intent.