DS knows in principle he is not allowed out alone but he's just started football and is mad for it and can't always be relied on to think first before acting.
Yeah. Kids can do that. That's why we pay babysitters. So there is an adult head between the kid and any impulsive things that might occur to them to do.
Otherwise we'd just happily leave them alone when we went out, safe in the knowledge that children come pre-packaged with an adult's mind and hard won experience, in a small body.
It's OK for a babysitter not to be breathing down their necks, micromanaging every tiny move they make. But they need to be aware enough of their charges to be able to notice that one of them has just hatched a harebrianed scheme, with their not exactly atypical 9 year old head.
She can't do that right now. She has a Big Thing preoccupying her. It is not just occupying her ear when she is on the phone, it is likely occupying a very large chunk of her headspace. So there is no room for anybody else, or their pressing needs when the Big Thing comes to the fore. Even when she is in sole charge of younger children.
She is a person in immense pain, dealing with something heartbreaking. And that is tragic. But when push comes to shove, she isn't well placed to consistently do the job asked of her, at the present time. Which creates a need for you to prioritise your children's need to be supervised enough over her perfectly reasonable desire to earn some money from you. When it comes to your kids the buck stops with you. It doesn't make you a horrible, unfeeling person to do what you are supposed to do and prioritise your children's needs over an adult's earning potential.