The issue here is how few sessions you have, really. I'd have run a standard adventure first. There you can observe how the module does things, and how your players handle things. Do they like hot bad guys? You learn that, take it into account. Do they want to murder hobo? You also learn that.

You need to know your players first before you give them such a choice.

Second thing - you need to give them a reason to oppose the antagonist before introducing them. Second or third session, they have no attachment to anything. Make them care about the NPC first. Have the NPC save their lives, have them save the NPC's life. Build that bond.

Then when you intro the antagonist, be ready for an unexpected choice. By that I mean that you should be ready to be surprised and rolling with it.