Not in the same situation, but my younger brother will be operating a vehicle soonish. Although my younger sister, yep, sounds just like her. But taking care of a pet? And driving? Not right. I hate to bring something like this up but is he mentally okay? Or is he just that lazy? It'd be terrible to part with the dog but I feel it would be best to prevent any harm coming to the pet due to reckless behavior of your sibling. Fault shouldn't be put back onto you because he doesn't care. I'd also like to know if he was raised this way as well? If my questions are too personal, don't feel like you have to answer them. I'd like to help and offer support if I can.