“Expected prognosis for cancer diagnosis”

My Mother in law was recently diagnosed with cancer. Her symptoms started with severe back pain, which led to a MRI that showed a tumor in her vertebrae, and possible lesions and metastasis. She went to an oncologist who ordered a PET scan and the results showed advanced cancer in her spine, lungs, liver (several lesions or tumors) and lymph nodes (several spots). The way she described the report was she has lots of advanced cancer in the above-mentioned areas. Her DR has ordered a liver biopsy to determine the source of the cancer, after which she will get a port and begin chemo. Her Onc told her he would use a chemo that she could tolerate, and would not be as harsh as some treatment with all the usual side effects. My MiL is 76, good health except for long-standing diabetes, which is well managed with a pump. I want to be able to support my wife through this, and at the same time have a realistic outlook for the expectations of treatment, recovery and prognosis. She and her husband are following along with Dr guidance, but I don't know if they truly realize the gravity of the situation. They are down in Florida for a few months and are expecting to return home to Michigan in May when all this treatment is complete. I expect those plans may change. Any insight would be appreciated and helpful. Thank you.