Dreams involving family members, like your mom and sister, can often represent your relationships with them or aspects of your own personality. In this dream, being at a "big rich guy's mansion" may symbolize feelings of desire for wealth, success, or a different lifestyle. It could also reflect a sense of being in an environment that feels out of reach or intimidating.

Your feeling of waiting in the car while texting them suggests a sense of frustration or anxiety, possibly indicating that you feel left out or disconnected from your family or their activities. The mention of school could signify responsibilities and the pressure you may feel regarding your education or future.

Overall, this dream might be prompting you to consider your current priorities and whether you feel supported by your family in achieving your goals. It could also be a reminder to communicate your needs more clearly, especially regarding time management and balancing leisure with responsibilities. Consider reflecting on how you can ensure that your voice is heard in your family dynamics.