Edel, this was so moving! It is a real gift to your nieces and nephews that they have you in their life. It surely enhances their sense of belonging and in turn their self-worth. I always feel bad for my kids, that they do not have any close uncles or aunts that dot on them.
Also, it is such a gift to your sister. Parents are always overwhelmed trying to juggle it all. Having a person that she can completely trust her kids with is priceless.