Another possible approach to the adventure (which I do not have, and therefore have not read) is for the party to arrive at Phandelver, rest over night, gather information, and then go after any other quest than trying to take down the Redbrands. If they went after the quest of Sister Garaele (is that her name?) who wanted help in going east-by-northeast up the Triboar Trail to speak to a -- what was it again? -- Yes! take a jeweled comb to Agatha the Banshee as a gift to mollify her, so the party can ask her about the whereabouts of a spellbook that had belonged to Bowgentle. There were other quests offered, too. If the party followed up on any of those quests, they might have reached 3rd Level before assailing the Redbrand hideout, and might have had a better chance. (If only it hadn't been for the "my way or the highway" Paladin.)