Question

Mary's brother has lived on a farm when he was small

Answer 1

Брат Мэри жил на ферме, когда был маленьким

Answer 2

It seems like there might be a small mistake in the sentence you provided. It could be rephrased as follows:

"Mary's brother lived on a farm when he was small."

Or

"When he was small, Mary's brother lived on a farm."

These sentences make it clear that Mary's brother lived on a farm during his early years. If you have any other questions or need further clarification, feel free to ask!