Before the baddies arrive:

Valance glances at the others and says "I'll hide on the other side of the bridge and make sure that the kidnappers don't try anything. I recommend that David stay on this side and prepare to shoot them if anything goes wrong." turning to face Falwell Valance adds "Falwell, let Dresil do all the talking. You can't bluff worth a damn." He then heads over the bridge and hides just off the path to the right of the bridge (towards the top of your map).

Spoiler
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Taking 20 on my hide check for a DC of 37 to spot me. Leaving my horse with the others, they can say its for the prisoner.