After giving it some though I think I might need a ruling on how ranged characters can help other player's character attack an enemy they already attack this round. I have provided below the actual rules for Ranged and Attacks so let me know if I am in the green or not.
So I was doing the Witch King quest the other day and well I'll just give you the turn by turn break down
Starting with Player Attack phase
Spirit passes -
Tactics -
Declared Boromir (+3 AS) and Gimili (+7 AS +1 autodamage) as attackers against the Witch King
They deal (7+3-6=4 +1) 5 damage to the Witch King
Raise threat by 1 to Ready Boromir
Lore -
Erebor Record keeper - Pay 1 Lore resource and exhaust to Ready Gimili
Leadership-
Declare ranged attack with Silverlore Archer against the Witch King
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*********Pausing Right Here********************************
In my game Gimili and Boromir joined the Archers attack based on the Witch King being assigned to the Tactics player. This allowed for the Witch King to be dropped in one round. I would like to think that is how it can be done however I not sure if the Tactics player can declare attackers without the Keyword ranged when it is not their active attack phase.
***EDIT***
It seems like the Tactics heroes would have to have the keyword Ranged to join in this attack. Which begs the question how does one simply attack the same dude twice in the same round?
(1.11) Limitations on Attacks
When a player is the active attacker during the combat
phase, the game rules grant him the option to declare
1 attack against each enemy with which he is engaged.
If, through card effects such as ranged, a player is able
to declare attacks against enemies with which he is
not engaged, he is still only permitted a single attack
against each of these enemies.
Characters are not limited as to how many times they
can participate in attacks against the same enemy,
provided each attack can be legally declared, and the
character is ready and eligible to be declared as an
attacker.
Ranged
A character with the ranged keyword can be declared
by its controller as an attacker against enemies that are
engaged with other players. A character can declare
ranged attacks against these targets while its owner is
declaring attacks, or it can participate in attacks that are
declared by other players. In either case, the character
must exhaust and meet any other requirements
necessary to make the attack.