Dreams involving fire often symbolize transformation, passion, or destruction. In your dream, the fire starting unexpectedly in a home that isn't yours could represent feelings of instability or fear in your current environment or situation. Since you were with your husband's brother and mentioned your mother-in-law, it may indicate concerns related to family dynamics or influences.

The sense of urgency expressed in your dream about needing to leave suggests that you may be feeling anxious about your safety or the security of your relationships. It might be helpful to reflect on any current worries you have regarding family matters or your living situation.

Consider discussing these feelings with your husband, as communication can help address any underlying stress you may be experiencing. This dream could be your mind's way of urging you to seek clarity and safety in your life.