You'll find some lamp oil in the general store (#7). If you're intimidating or open to bribery, then you'll be able to convince him to help defend the village. After learning that he was paid to spy on the castle, you'll be able to force him to help with the village's defenses. They'll give you some minor tasks to complete, and you'll find some other possible defenses as you explore the village: Teagan will direct you to meet with Murdock (#3) and Ser Perth (#13), who have been organizing the village's defenses. After tending to Teagan's wounds, he'll ask you meet him by the mill (#14). The undead will then storm out of the castle and kill everybody except for Teagan, who you'll find unconscious in the chantry (#2) when you eventually return. To do this, you'll just need to leave the village before triggering the battle (regardless of whether you said you'd help or not).

You can leave the villagers to their fate.

You'll have two options for how to respond: Teagan will then try to convince you to help defend the village. Lothering that Eamon is ill, but when you arrive in Redcliffe you'll find out from Tomas (#1) and Bann Teagan (#2) that the village has other problems as well - undead creatures have been attacking each night, and nobody has heard anything from the castle in days. You'll need to visit Redcliffe to recruit Arl Eamon and his human soldiers to your cause.

Note: If you arrive in Redcliffe with Alistair, then he'll reveal that he's an illegitimate son of King Maric, which means that he's a possible heir to the throne.

Dragon age origins redcliffe