This is completely, completely shite for you. However, my dear one, I am going to be a little bit robust: no-one else is stepping up to take care of you and your DM at the moment so you have to step up and take care of yourself.
First, get up, have a tea, go for a walk, eat some food. Something really nice, whatever you fancy. DM is in hospital right now, so she is safe and cared-for.
While you're having breakfast, make a note of anything you want DB to actually do. Yes, he shouldn't have to be told, but he's being useless so tell him. Even if it's to come in and do a three-hour sit with DM every evening while you nip back to shower and eat. You need the break, he clearly needs the structure.
When you go into the hospital today, ask to speak to the palliative consultant. They should give you a clear idea of what's happening/what might happen next. Obviously the goal is to get DM into the hospice asap and the hospital will be working towards that. Once she's in the hospice, a little of the pressure will lift as it's such a different environment, where they are also a little bit more geared towards looking after the family as well as the patient.
Please stay hydrated and keep eating. The process isn't pleasant and I have first-hand experience of this specific cancer, but once she's in the hospice - they are so kind and experienced and they will hold your hand through it.