Hey - it's hard to watch a loved one suffer. The drugs really do sound like the reason he is so out of it... Try not to worry about the biopsies. Cancer is a one day at a time thing. As stressful as it is try not to worry constantly it's not good for you either. Especially because you have other loved ones that depend on you.
It really dies sound like his lack of motivation could be drug related and maybe he's a bit depressed to. but you wouldn't know that until he's drug free. Good luck and many blessings to you.