so sorry to hear this. Lost my sister to a brain tumour last year. Her XH was very supportive, especially with the children. In fact, his whole family were great. Don't read any further unless you want to know my experience.
One of the first impacts was "cognitive impairment" - their term. This meant she developed very poor concentration and short term memory. I went to every appointment with her. The consultant said the grade of brain tumour is almost immaterial - it's the location and rate of growth that they monitor. She was grade 2, but quickly developed 2 new grade 3 tumours.
The surgery went well. They debulked two of the grade 3 tumours significantly (can't remove brain tumours completely as that would mean removing brain tissue apparently) but couldn't touch the first because of its location. Prior to surgery she was having many fits each day and had tremors down one side. These immediately stopped and she recovered total mobility in her left arm and leg. It was amazing. But she still had the three tumours.
There is a gene they test for that determines if treatment is likely to work. Sadly she didn't have it. She had a debilitating course of radiotherapy followed by chemo. With hindsight, we probably shouldn't have gone ahead with it knowing it was unlikely to work. The radiotherapy was painful and led to numbness which affected her mobility with the result we had to get a wheelchair. It also affected her eyesight beyond correction with glasses. She gave up on the chemo after the second round - she was so sick and contracted sepsis. The advice was it wasn't helping.
She deteriorated quite slowly. She had quite significant personality changes - from being very social and friendly she became very aggressive. She was very nasty to her children (young teens). She picked arguments with everybody. This is common in brain tumour patients. The drugs made her very sleepy - she could sleep for hours then be wide awake during the night.
The Brain Tumour Charity has lots of helpful advice. I found the McMillan nurse to be tremendously supportive - as was the neuro-oncology nurse. There was also a Maggie's Centre and support groups but as she lived very rurally and couldn't use transport on her own (I live 200 miles from their home) then she couldn't use them.
OP, if you're still reading, I'd do the research so you know what to expect so you can support your son, but also yourself. It's devastating news. It's a cruel, bastard of a disease. Take care of you.