I think she deserves to know

ya mate, el bani begool:
من حسن إسلام المرء تركه ما لا يعنيه
i dont think anyone has the right to meddle in, and if i were that sick person i would weight the outputs of my actions, what good can it bring if i tell her or not? i cant think of any reason i wouldnt tell her for even if shes aging, el a3mar beyad ellah and family are for each other, but then again, thats not my decision

when i was terribly ill i did not even tell my sister who lives in the same city. i put on a mask and hid everything. it serves no purpose seriously. plus it will make him feel worse imho. he will feel some sort of guilt that he will have so much agony dealing with.

its none of anyone's business but his own. if he wants to tell. thats his decision to make. not anyone else's..

It depends on how healthy she is (wouldn't risk giving her a heart attack), and if he needs her by his side. Honestly, I don't know if I would tell her- at least I would prefer not to be the one telling her. I am a coward when it comes to telling bad news to anyone...

I think it depends on many inputs; do they both live in the same city? How old is his mother, being old does not mean she could not handle it although of course it might be very difficult? etc.  In short, this is a decision that depends on the situation at hand. For sure it is not an easy decision and I am sorry I really don't know what would be the best thing to do.  

As my friends said it depending on many things

I can add that, if her knowledge wont make any different  and it will not ease it on the sick family member,I don't prefer to break her heart...

Honesty is the best policy...and she is bound to find out one way or another.  Mothers know, call it sixth sense.  I call it a direct line to the Man upstairs who know the love they have for their children.  They know...or will soon enough.  Mine at 7000 miles away knows, when she's 750 miles away she knows, and when she's in the same house as me she knows.  How would she react if she knew others knew and hid it from her.  This is a matter of life and death.  Each conversation could be their last...she needs to know that...and it is unfair to withhold it from her.  I am sure she is wise and has seen a lot in her life....and if she's anything like the women in my life, he is very strong; emotionally and spiritually.    I would doubt she is as frail as people accuse her of being. It is afterall Gods will.  

Why would I talk to her? I tend to stick to my own generation. But there's no reason why she shouldn't know. It might give her a sense of purpose, to worry.