Hi, I am so sorry to hear about your situation and send my best to you all! I would suggest spoiling your little boy rotten, show him how much you love him and give him all the sardines he can eat!
On a more serious note I would suggest making him a safe space, a den almost that is super comfy and warm, with his favourite blankets etc so he can feel safe and comfortable. If you suspect he is in pain or discomfort your vet can prescribe medication to make him happier. Hang in there and appreciate the time you have left!
My thoughts are with you at this time. ❤️