So sorry to hear this. It sounds like you love your kitty very much.
I cannot tell you what to do, but only what I would do.
Our other 2 cats have cut him off, and in some ways it seems cruel to make him go through this trauma (again).
With so many tumours, especially the huge one on his liver, I also think it would be cruel to put him through any aggressive treatments and I would not do it. Quality of life is more important than quantity, IMO, if treatment is going to buy so little time that it's not worth it.
Again, so sorry. We all know how you feel.