life span of lung cancer patient with multiple brain metastasis

My husband is afflicted with lung cancer for almost 5 years and with 7 brain metastasis. He was givenchemotherapy, radiotherapy and oral medications for his lung cancer, and was also subjected to brain radiotherapy. However, after follow up MRI, his brain cancer is bigger compare to his previous MRI. He is already bed ridden, cannot stand, move and look after himself and shows difficulty of speaking and sleeping. He cannot write anymore and have a hard time in expressing himself because he dont know the word to say, he is also slurring when he speaks. Can you please give me an idea how much time is left for him. Also, he can only consume around 5 tablespoons of food but more on liquid.