Inlaws

In-law are extended family members of spouses who become related by their marriage. The term would cover to varying degrees of relatedness:
 * Brother-in-law
 * Daughter-in-law
 * Father-in-law
 * Mother-in-law
 * Sister-in-law
 * Son-in-law
 * Cousin-in-law
 * Uncle-in-law
 * Aunt-in-law
 * Nephew-in-law
 * Niece-in-law

Technically a spouse, wife, or husband is an in-law (the closest in-law) but is often not thought of as such.