Plot

So:

Tenchi and Gohan in the past are born with powers that make the Goddesses interested in them. They allow the boys to face the Triad hoping one or both will prove to be the power higher than them that they are looking for. They fail, however. Washu, in an attempt to seal away the Triad, has to also give up her powers. She turns into a humanoid and spends 20,000+ years in the third dimension, where she meets her husband, has a son, befriends Naja, clones Kagato, and creates Ryoko and Ryo-ohki. Her powers and essence are the gems that she gave Ryoko, but she can not use them fully, at least in her current state. Washu cannot use them either due to her becoming the entity we all come to know. When the time comes, Tokimi is able to release the seal on her sister since her powers are no longer holding the Triad prisoner. She had to wait to do this because she still wanted to find the beings. Her powers are basically split up between the three gems, holding the Triad in place, and Washu herself though the last one has the least amount of power. What about the gems? I don't know to be truthful. In the anime she is able to turn into her Choushin self and tells Tokimi to release her and Tsunami because they need to contain Tenchi before he rips the universe apart with the powers he is not ready for. Anyway, I'll just say they have her power, but they are not the sole source or container of it.

The boys are reborn thanks to Tokimi though she keeps this from Tsunami. Their powers eventually catch the Goddesses' eyes hence their interest in Tenchi and Gohan (from afar). The key to controlling their powers is being well-rounded (having all four virtues). They use this to beat the Triad finally. At the same time, their powers are not given to them by the Goddesses because they cannot create something more powerful than them. They cannot even beat the Triad. All they can do is contain the beings as explained, but this even fails eventually. So why do they have these powers if they are not the higher beings? A lot of fans have speculated on the real version of Tenchi being an avatar, a manifestation of the kami in this plane. I rather like that idea so I may hint at it. Maybe.