The two of them are insanely close to an almost freakish level. At times they could be considered one person and they often think of themselves like that. This is because of the very strong Force Bond between the two of them that, when they are close together, allows them to mentally blend into one sort of joined mind. In fact the reason why the two of them have always been so close is that the two of them are one person in two bodies.
However, despite this, Trever is different from his twin, most visible when he's separated from him. He tends to be more aggressive and has more dark side tendencies. This is because he embodies the Dark Side of the two of them, Kale the Light Side.
When the Twins' thought their father was killed by the Empire, he left home and eventually ran into a Dark Jedi, Kree'sha, who took him as her apprentice, encouraging his dark side tendencies. Eventually, he left her though, on his own or by her order is unknown and returned to Kale.
Trever is murderously protective of Kale and really his only real loyalty is to his brother.
Currently he lives with his twin and Tobias force_killer while the rest of their family - the non Force Using part of the Delvar clan, live near by in the Nexus.