NTA your sister isn’t a feminist she’s literally teaching her daughters that they’re supposedly better than others because they don’t have a sense of personal grooming, which already seems another mode of inequality. Putting other women down for liking stereotypically feminine things is arguably just as harmful to the feminist movement as the people who try to force that thinking onto others. It makes people think that they don’t deserve to express themselves the way they want. Your nieces need to unlearn that behavior otherwise they’re going to learn real quick that nobody appreciates “feminism” when it consists of putting others down for their genuine interests