Hope things are going as well as can be expected under the circumstances. My parents had to go from Michigan to Minnesota for my sister's treatments. Usually one parent had to stay home and work while the other stayed for the week with her. So the family was literally torn apart physically by the disease much of the time, but they would take turns and make do. Somehow you learn to get through it. I was already at college when it happened and they did not want me to come home and stop my life. The same with my brother, so they took on the burden with the help of their extended family.
When a child has cancer you think that the worst thing possible has happened to them and to you. But I always remember this story my parents told me about my sister being in the hospital. A boy about 10 or 11 was on the same hospital floor with her. He had a rare disease where his bones at the elbows and knees just kept growing so that eventually he would just keep having to have surgery to cut them down because they would have grown through his skin. Horrible enough, right? But the sad thing was he had absolutely no one there to help him through the situation. A social worker would check in on him from time-to-time, and the nurses gave him extra attention, but no parents were ever around. According to him his mother was a recovering addict, and his father was in jail for abusing him.
So the point is that people go through some amazingly horrific things, and they even have to do it alone. Your providing support for him and his mother will make WORLDS of difference to them. Your job couldn't be more important, and it doesn't matter how well you think you are doing it. Just by attempting to be there you are giving something that other people long for desperately. That is a success in itself and you can be sure that they will appreciate every moment of your time and every bit of your love in the future. You are doing great.