Unless your daughter who is job hunting has child-care five days a week she will be severely limited in what jobs she will be offered, so she needs to sort that out as her first priority.
She is also being unkind as her brother-in-law's health is apparently the reason that her sister needs your help with child-care right now.
If they were my daughters I would help the girl who has an ill husband, right now, and tell the other to be her age. She has had years of child-care out of you, now it is her sister's turn, and she can like it or lump it.