That doesn't make sense, you have been saying that Tarquin is his brother (Taroyn) you can't change who he is now. 

I think what you are trying to say is this:  The essence of Tarquin is in the crystal and Taroyn uses it to make his life easier as a mask to get around and live a semi normal life. When he takes off the crystal/the mask and shows himself (Taroyn) he has his own set of powers. Whereas he can only use his OR Tarquin's depending on who he is looking like at the time because as a life essence Tarquin has his own set of powers and memories.

Have I got that about right?

[@Marcus XVI]