60s is not elderly or vulnerable
People of any age can be vulnerable if they are not well but it doesn't make them your responsibility.
When my new next door neighbour had a stem cell transplant and her sister had just moved abroad, I visited her every other day because I could and she was immensely grateful.
I wouldn't have done the same for someone who expected it of me.
Now my neighbour is better, we are the best of friends and as I sit here typing this, her dog is in my garden because I am looking after her for three days while my neighbour is away.
Even if I refuse my neighbour will insist on paying me for looking after the dog.
I have tried to refuse but the reason why she pays me is because she would rather I had a bit of extra cash than the dog go where she used to.
At the other dog sitting place, the dog was often left alone all day in a kitchen with other dogs and she didn't like it there.
In my home, the dog becomes part of the family for a few days.
Any way moral of the story is that some people in life are grateful and appreciate your help and other people don't and make you feel as if you should do things for them because you can.
I think that the two sisters in your road fall into the second category.