Alexandra i'm so sorry you have to go through this and you're so young. Your story sounds very similar to mine. I'm 32, my mom passed away in Jan. 2003 from lung cancer. On Christmas Eve 2001 my mom had a seizure...in the ER and a few hours later they told her she had a lung tumour and a brain tumour. A month later she had surgery to remove the brain tumour. She was "lucky" enough that it was operable. They started her on various chemo treatments after that, which were successful for a while. However, she had a stroke in Nov. 2002, paralyzing her right arm and simply got worse over the next couple of months until she passed away.
Brain mets are unique to each individual due to their size and exact location. There are chemos designed for this but I don't know how effective they are. Have the doctors considered surgery or radiation? Brain mets are usually not painful...if there is pain or discomfort it is related to the way it affects the part of the body that is controlled by the location of the tumour...ie movement, speech, sight, etc. I wish i could give you more info. I hope at the hospital you will be able to speak to a neurologist/neurosurgeon who will be able to give you more information but i would by no means say that this is the final stages. If they are able to do something for his brain mets then he certainly can continue his fight against this disease. Each case is different.
A woman who was in the bed next to my mom had struggled with recurrent metastatic lung cancer for 6 yrs! The doctors initially gave her a few months and 6 yrs later she was still there! I certainly understand where you're coming from and I will keep you and your dad in my prayers. Love him, hold him, kiss him, hug him as much as you can.