End Of Life Cat Sitting

I've been looking after the lovely Alice (7 year old cat) for the past six years. Her owners have just told me that she has a terminal diagnosis but they are going away in a few weeks for three weeks to Disney USA (I'm in the UK). They're unable to cancel the holiday and have asked how I feel about looking after her (drop in visits, twice a day) under these circumstances. I don't have a problem with this but not sure what agreements to put in place to cover so there's no misunderstanding. I was thinking of asking the owner to give clear instructions to her vets. Also if I find her in poor health, out of normal working hours, do they want me to take her to the emergency vets. And if she does pass away while they're abroad, should I have her cremated etc. Any thoughts or suggestions please?