It is possible to win this quest with 4 players, but the decks have to be designed to be prepared to it.
In my play group we beated it with the following heroes:
A- Beorn, Hama, Legolas;
B- Boromir, Glóin, Glorfindel (spirit);
C- Brand Son of Bain, Thalin, Dain Ironfoot;
D- Bifur, Eowyn, Eleanor