What should I do with my nosy sister?

The most direct way is to discuss with your husband for a period of time. You two move out and let your parents-in-law live by themselves, so that your elder sister-in-law will be honest and won't interfere in your family affairs any more.

But what should I do with my in-laws, and what should I do with my in-laws? After all, they didn't say anything. It's right to be filial to them, because after all, your husband is an only child.

But you must be firm with your sister, don't be soft-hearted, don't give her face and treat her as a stranger, so that she will never interfere in your family affairs again.