This is a sad situation and l think all you can do is go with her parents wishes. They must be in pieces.
l can reassure you that The Hospice at Home Care is second to none. They also care for the whole family and although there are some confidentiality issues they can
talk to you and give you accurate information to allay your worries. Why don't you give them a ring? it will be helpful. You could start by going on the hospice's website.
The other things are to busy yourself with things that would support you son and Dil - food, looking after dog etc
l do have a good friend who, with her husband, nursed their young daughter through terminal cancer, at home, and the worst was her having lung secondaries. 2 years on her mum gets flash backs, has withdrawn from everything socially. All we can do is keep in touch by text as she doesn't want to meet. l bump into my friend's mother ( daughter's granny ) and she talks to me because her daughter is so bereft contact is very superficial. She feels hurt because she is grieving too. Like you she just has to hang in there and be there for them. Its an awful situation for you but worse for her parents.
xxx