Mindsets are defined as people's beliefs about the nature of intelligence, and previous research has found effects of students' mindsets on their academic outcomes. In the present study, we bring together two recent lines of mindset research: research that has demonstrated that the mindset contexts that surround students matter above and beyond students' own mindsets; and research that has demonstrated the importance of parents' mindsets on students' academic outcomes. Specifically, we explored associations among the "family mindset" context--operationalized as undergraduate students' perceptions of their parents' and older siblings' mindsets beliefs about math ability--and their motivation, behavior, and affect in math. We found that students' (N = 358) perceptions of their parents' and older siblings' fixed math mindsets were negatively associated with their motivation, engagement, and help-seeking behaviors in math. These findings underscore the importance of family mindset contexts to students' math motivation and engagement, especially the role of older siblings, which is a particularly novel contribution.