Therianthropy refers to a physically human being who strongly identifies with a physical animal (past and present) on a psychological, behavioral, or spiritual manner. In essence, a Therian does not feel they are completely human in those aspects, though physical shifting and DNA of anything other than human is typically shunned by the majority of the legitimate Therians (lots and lots of bad apples, as many here can relate to with just about any practice or belief). There is an element of shifting, though it is psychological, behavioral, and/or phantasmal and can be spiritual or mental in nature.
Kinship is similar to Therianthropy in that a physical human identifies as not completely human, though the difference is that the Otherkin refer to entities that have never been and are not physical in nature. In ancient lore across the globe, kinship has existed in humans of spiritual ancestry. It is mostly in modern practice that we know of people who identify as having complete spirits or souls of beings who are not human.
Starseeds, Indigo/Rainbow Children, etc. are completely a New Age thought. Because it has no stance in tradition, less people take it seriously. However, that does not mean they do or don't exist. It merely means that is a new concept.