Ok this should be simple,
Action = Lay
Price = I would set at the lowest of your threshold (
Amount = 2
Markets = Horse Races
Status = In Play
Selections = First Matching Selection
Conditions = are met
Any selections Lay Price is between 8 and 10
and Favorite's Back Price is between 1.01 and 2
and Second Favorite's Back Price is between 3 and 5
Cheers
Rich..