I got an official response about "Forth Eolingas," which I'll post below for any interested. Because the card is worded that heroes can "declare attacks," I was curious if that meant they could participate in each other's attacks, how other characters could interact (if at all), etc. Here's the reply I got:
Caleb's response follows:
Forth Eorlingas only allows Rohan heroes to attack enemies in the staging area. Non-Rohan characters cannot participate in these attacks, but you may declare any number of Rohan heroes you control as attackers against a single enemy in the staging area. Your friends cannot commit their Rohan heroes to your attack because it's not their attack window. The Ranged keyword does not work during these attacks because the rules for Ranged only apply to enemies engaged with a player.
Hope you enjoy riding down your enemies with the new Rohan player cards!
Cheers,
Caleb