If we can stop the oil attack, it will save us a lot more hp than the shield will. You are one of the quality ranged attackers too.
With that said, it'll only work if everyone works together. 3 people together needs to work the ram, and Eduardo and Gruunk have already said they will work the ram. If you don't help, they can't finish that plan.
In the end, you four are at the gate, Fortune is working on the side, killing the archers. She can't discuss in-character with you, and you need to reach a decision shortly.
Just letting you know: It will probably take several rounds to break down that gate, and the kobolds can do a lot of damage to you in that time.