I may be out of date on this subject and some of the following won't apply, or not yet, but:
check the GP and social services are regularly involved. If he is assessed by SS, and gets in the system, he can get carers and occupational health aids, and physiotherapy, so your mum does not become too exhausted. I'm sure there must be someone on MN who knows the uptodate position. Your mum may not want strangers in the house, but push for it when you see her struggling.
You will need to monitor the situation as much as you can, check the carers are turning up, check that he is fed in hospital, check your mum is sleeping, check she has help with the shopping etc. There is sometimes a prescription delivery service. Maybe order online shopping for her. Food and clothes. Ready meals can be delivered to the door. Sit in with him to give your mum a break. Take them out in the car to get them out of the house. Talk to your mum and find out how she is coping. A third party observant eye (yours) is essential to watch how life could be made easier for them, eg, oil that door, organise shopping etc. Get a battery alarm system/bell so he can call her from his bed when she is downstairs.
St Johns Ambulance used to and may still run courses on moving and handling, first aid, and a carer's support group.
Make time to let him enjoy you and your family. You will regret it forever if you don't and its too late. If he hasn't much time left to be fit, he is a priority for you now. See lots of him now whilst he is still fit and you can remember him as fit. Get out the old family photos and ask him all about his early life, and their courtship, his parents, and all sorts of family history that is only in his head. What about Skype to let him keep involved with the children's lives.
You will have heartbreak. But the more you are able to help them, the better you will cope.