We are going to "cat-sit"

and it is an alarming thought. 
Nephew and partner are moving house today - instead of going on a honeymoon. They have a cat. Said cat will be in the way or - more likely - run off and not be able to be found. 
They are very fond of the cat - and  yes, the cat is thoroughly likeable.
Middle Cat, Nephew's mother, has two cats. They strongly disapprove of any other cat. There is no chance that young H.... can stay with them.
We have not had a cat in the house for twenty years. It was a conscious decision. Our last cat lived to almost twenty-one. The Senior Cat would love to have an animal around the house but we both know it isn't practical or safe. He will be acutely conscious of an animal who is only staying for a couple of days but even so I am feeling rather anxious. The Senior Cat is not steady on his rear paws and he is likely to trip over four small paws unless he is very careful. 
The Senior Cat would like a golden retriever dog or a Burmese cat. We certainly couldn't manage a dog - neither of us could walk a dog and we both believe that dogs need walking at least once a day. Training and grooming a dog takes time and energy too. I don't have the time and the Senior Cat wouldn't have the energy.  At least there are mobile dog washing facilities these days.
And yes, I know cats are very independent creatures but they need to be entertained too. We never had a problem with our cats catching birds. They had too much exercise and entertainment for that but could we do it again? I don't think so. A well cared for cat also needs to visit the vet and we don't have any means of getting a cat even to the closest vet. 
So, we don't have an animal of our own any more. We won't have another one.
But can we manage to cat sit for a couple of days? I hope so. The forecast is for extremely warm weather (36'C) so the Senior Cat will not venture outside - or should not need to. It means I will be less concerned about young H....escaping. I may need to put a notice on the front door warning potential visitors of the presence of young puss and ask them not to let him out.
And I have taped the cat flap shut!