My parents were waiting in the queue to buy museum tickets. My brother and I were queuing up for ice cream.

Although my parents were waiting in the queue to buy museum tickets, my brother and I were queuing up for ice cream.

As my brother and I didn't like visiting museums, my parents chose to queue up to buy ice cream.

While my parents were queuing up for museum tickets, my brother and I were waiting in the queue to buy ice cream.

My parents were waiting in the queue for museum tickets, but my prother and wanted to buy ice cream.