Hi Nakita. Please feel free to vent here any time you ened to. You have so much on you plate right now, you need an outlet. My heart aches for this little guy, and how scared he must have felt when in pain. Thankfully he has you and your husband.
Contact the local chapter of the American Cancer Society. They can help arrange transporation to and from appts, and I think they can arrange it cost-free. Are you near a large city or a small town? They do such a good job of matching All different kinds of programs/assistance to all the needs of cancer patients; that's what they are there for. Being the guardian of this child and his sister, you are entitled to assistance in their care, be it for drs appts, meds or transporation or other things. Use them!!!
As I read your post I kept hearing the bells of an angel getting her wings. You are an angel
and this family is VERY lucky to have you. You are the only glue holding them together right now, and even tho they don't show it in the nicest way, they know it. That's why they turn to you, when they are in need of anything, from reading info to them to adminisitering medicine.
Through all of this, take care of yourself. Your husband and children need you too. I'll see if my friend (a nurse) knows of any thing else you could check in to.