I don't know what his original sentence was so I can't give you much information on your question. In general a prisoner will serve a certain number of specified years before he is eligible for parole. That does not mean he will get paroled the 1st time he goes before the board. With a charge like murder he could make many appearances before the parole board before getting out.
Obviously if your friend's parole is being refused and he is receiving 2 year set-offs (that is what they are called - meaning they will not consider his for parole for another 2 years), then he is eligible regardless of the number of years he received.
There are two methods of which I can think of to get him out: hire a parole lawyer who will know what types of information (besides having 2 nice homes) will persuade the parole board. More than likely he will first go to a halfway house if he has been imprisoned for so long. In addition, my guess is that his conviction is for capital murder since he continues to be refused for parole. It is best to have advise from someone who essentially specializes or focuses on that type of work.
The second method is to attack his conviction by filing an application for writ of habeas corpus (if an investigation determines that it is appropriate, and if he has not previously filed one. Except in very limited circumstances, a Texas state inmate is allowed only one writ.)
It would help to have letters of support for your friend, as well as proof that someone will hire him whenevever he is released. I'm sure that a parole lawyer could help with additional ideas, including perhaps reviewing the original offense report to determine if there were special circumstances which lead to the killing.