I've got an idea for the brass plate relay:

You could have the kids start at one end ladled "the cave" and have them race to "Laban's House" where they have to grab a picture cutout of Laban or the guards and run back.

• Then a group of two from the same team have to run together to "Lehi's House" (which is right next to Laban's house) to pick up the "gold, silver, and precious things" (little cloth bags of marbles maybe?) and bring them back to the cave.
• At the cave they hand them off to two more members of their team who then run them to Laban's house, dropping them off before running back.
• Then the last member of the team runs alone to collect the plates and return them to the waiting team.

I hope this makes sense. I made it up as I went along. :o)

You would have the plates and the cutout pictures at Laban's house and the bag of "money" at Lehi's. I would have a separate group of houses for each team to avoid collisions and confusion.