First, you have much reason to be proud. You have done a wonderful job raising a fine person. Your son is kind and loyal; it is a wonderful combination of
traits. It sounds like he has the maturity to make his own decision about what role he should play in caring for his grandmother. To make such a decision, however, he needs information. He should be told about his grandmother's illness and how it is likely to progress. It is important that he understand what complications are likely and what will be needed from her caregiver. This information can be provided by her physician or perhaps by the people at Hospice. Several questions also need to be addressed. The first is whether it is best for your mom to be at home with a family member, or whether she needs more care than can be provided in her home and would be better served in a facility with 24-hour professional care. The second question is what would your mother prefer. The third question is whether your son has the knowledge and psychological tools to manage what is required of his grandmother's caretaker, and whether this is in his best interest. Once the two of you have the answers to the first two questions, your son will need to think through the answer to question 3. I would strongly encourage him, perhaps with you, to get advice from people he trusts, from the professionals at Hospice, and/or to consider a session with a mental health professional to carefully evaluate what is best both for his grandmother and himself.
If your son decides to be the caregiver for your mom, I would encourage you to get information about respite options that would give him some breaks from caretaking. This includes some breaks during the day so he can replenish his energy. It is also going to be critical he have some help at night if she is having trouble sleeping. No one does well if his or her sleep is persistently interrupted.
In order to decide whether to accept Hospice care, I would suggest you and your son meet together with someone from Hospice. Hopefully they can explain to him what is it Hospice has to offer. They are experts in helping people maintain their dignity and comfort through a process that can be harsh and painful. I would anticipate that once he understands their intent, he will be more comfortable accepting their help. If he decides against using Hospice assistance now, at least he will know what could be available down the road.