Playing the game last night for the first time and a situation came up that led to a pretty sassy argument. A player set marching orders in 2 adjoining territories. He moved a footmen from Yronwood into The Boneway, where there were another footman and a knight with marching orders. He then tried to take all three units and attack Storms End. We argued that was an illegal move because that would be moving 1 unit twice. The rules a re a little unclear about it. He found the section on staggered attacks and used that to justify his move. Please help. I would hate for him to stop playing this game with us.

He was right. There is no limit on how many times a unit can move in a single turn, as long as the unit moves to where another march order is and is still within the supply limits.

The Rules are NOT unclear, and the section on "Staggering" March Orders is exactly the place to find it:

Advanced Strategy Tip : A player can “stagger” movement by
placing several March Orders in adjacent areas. In this fashion,
a unit is able to move more than one area in a turn . This is
accomplished by marching units into an area containing another
friendly March Order, and later (when resolving that second
March Order) moving that area’s units into a new area (potentially
containing the third friendly March Order, which would allow
the units to move again when that last March Order is later
resolved ). This can be a difficult trick to accomplish, however, since
a successful enemy attack could remove one of the March Orders
in this chain.

We did look at the section Kauai, and the thing that I pointed out is this sentence

This is

accomplished by marching units into an area containing another
friendly March Order, and later (when resolving that second
March Order) moving that area’s units into a new area (potentially
containing the third friendly March Order, which would allow
the units to move again when that last March Order is later
resolved )

The problem I have with this is why does it say THAT AREA'S UNITS can now move? If all the units could move, wouldn't they just say that? It reads to me that only the units that have not moved yet could then move to not have to use a power token to save the vacated territory.

"that area's units" means the units in the area (which includes the units just moved there). There is nothing unusual about the use of "that". Look at "that second March Order" and "that last March Order".

When in doubt about something that is NOT clear, look to the phrases that ARE clear:

a unit is able to move more than one area in a turn

allow the units to move again