[TLFisher]

Generally I see the FTT as a rite of passage usually for college graduates who want to show how absolute for the local churches and Living Stream Ministry.
Though I lived with brothers who went through the full time training, I am years removed. I would recommend the insights of the poster 'Freedom" since his involvement with the local churches is probably more current and more precise in analyzing the perils of full-time trainees.
Best analogy I can think of Full time training is the Mormons and their missionary service. More serving to the organization/sect than it is benficial to the individual. There's no promises of full-time support once the training is completed. One may be expected to compete for employment in the work force just as everyone else does.
In response to your questions:

"1) I need to know what it means that he has joined the FTT? Is there any hope for him and his mental and emotional health? "
Each person is different. Brothers I have known became quite distant following the full time training. All semblance of their personality I knew prior to FTT was absent.

"2) Can someone please explain how one can claim to "know the truth" and "have the light" and yet their lives are in complete darkness and chaos? How can he not see that?"
A one word answer, deception.

"3) I need to know what the FTT means for him and how I can walk away and stop hoping for him to change if he never will. I need to be set free from this mess."
Seems he needs to be the one to answer the question. What does he hope to gain upon FTT graduation? Is it merely one process in achieving LC ambitions?