Sorry for the news and for what I'm about to write.
(English is not my native language).
My son (stepson actually, but for me he was a son) died 2 months ago from a glioblastoma. He was 16yo when diagnosed and spent 16 months in chemo and radiotherapy.
All the time spent on treatment was absolutely necessary, doing something is surely better than doing nothing at all. He was given about 6 to 9 months to live... He lived 16 months.
One thing that I must ask you to do is to appreciate EVERY single moment that you have now with your mother, don't take nothing for granted, nothing. Every moment will be a memory, every word, expression, laughter, anger, everything.
Just keep in mind that if you do this, the "last call" will be yours/your father/your brother.
I don't how how this works in your country, but where I come from we have paliative assisted cared, wich is basically making sure a terminal pacient is "confortable" to die (basically a lot of opiates and muscle relaxants") wich is only administrated when the family agrees to (there is no assisted suicide/euthanasia here).
My son always managed to recover from basically anything, he had seizures and recovered, had neurological hiccups and recovered, had multiple infections and recovered, changed chemo and reduced 50% of the tumor, never felt sick, always had amazing recovery capabilities.
1 and 1/2 months prior to his death he started to show some afasia and short memory problems, until he had a grand mal seizure (while medicated for epilepsia) for 1 hour, being the longest time seizing of 17 straight minutes.
The tumor had grown and was not responding to treatment, but sill my son managed to recover from the seizure. When he woke up after the seizure he wouldn't speak, recongnize my wife or me, couldn't control any function whatsoever. But in 3 days he was speaking, reading and writing.
Hope got the best of us and we felt that we would have time for another treatment, but we we're wrong.
He had another seizure and never recovered.
We saw him losing the ability to read, speak, move. After that he lost his sight, ability to recognize anything or even respond. But from time to time he would give us a kind of sign that he was there (at least that's what we thought it was).
The doctor told us about paliative care, and we on first hand refused and got very angry at him for saying that... He would recover, we were sure of that.
Everything only got worse and we started to notice pain in his expressions, that's when we knew that the doctor was right. The tumor spread and was invading the meninges.
We started paliative care, he didn't ingest food already for 2/3 days.
In 3 days we witnessed him lose the ability to urinate, make any noise and then his heart stopped followed by the last breaths.
The reason that I write this and explain all this in this way, is because the only thing that I don't know is if we made this decicion of going into paliative care too late... Was he suffering already and we didn't notice? Did some pain expression got by us because we were always hoping that he would recover? Did we fail to do that?!
THIS is what you will have to be prepared to live with if you go with this. You will have to make the decisions necessary, and they will be necessary...
Watching someone lose their brain capabilities slowly is horrible, and most of all it's frustrating because there is nothing you can do to stop it, you will feel terrible and you will have too make the decisions for them.
I always question if any of it was worth it, if we should have gone without treatment from the beginning... But we had 16 months, we were able to travel, laugh and have new memories with him that we won't forget. And that matters.