With a small business - which this is - "considerable" is defined as only about 15 hours per week. This would not preclude your Brother having another full-time job (many small farmers do) or running his own farm as well. It might also include time spent on paperwork, form filling etc. Additional evidence would include use of the land by your Brother to store his own cattle/sheep etc. However this is definitely a case where it is worth consulting an expert. It will be money well spent.