Explanation:

- My niece is very kind and ______ to everyone in the family.

- This sentence describes someone with qualities that convey warmth and positive regard towards others.

- Option 1: Callous

- Callous means showing or having an insensitive and cruel disregard for others.

- This option doesn’t match because it contradicts being kind.

- Option 2: Generous

- Generous means showing a readiness to give more of something, such as money or time, than is strictly necessary or expected.

- It complements "kind" well, as both are positive traits.

- Option 3: Stern

- Stern means serious or strict in manner.

- Although not necessarily negative, it doesn't align with being kind.

- Option 4: Ruthless

- Ruthless means having no compassion or pity.

- It conflicts with being kind.