planning to visit my sister in law who has a chinese citizen husband

Well, if your sister works or studies in China, you can apply for an S2 type. If not, you may apply for a Q2 type. The required documents are your passport and its copy, an application form attached with your recently-taken photo, the relationship document, and an invitation letter from your sister or brother-in-law, and a copy of your sister's residence card or her husband's ID.