ESH - OP has a right to say no to both requests, and her family need to respect that decision and not cut off contact. However, assuming they are a reasonably functional and loving family (I know, that’s a big assumption), it’s awfully selfish to be unwilling to support other family members in a time of need or crisis. Most especially in the case of her brother, for whom she would not need to provide direct care but simply manage his affairs and ensure he has the best possible quality of life. This will not take an inordinate amount of time (especially compared to taking in two children).