Confused about how to handle social encounters in 5th edition? There are actually rules about it, here's a quick and easy overview.
First, determine the NPC's initial disposition. For allies of the party this can be Friendly, for any enemies it should be Hostile, and for everyone else Indifferent is fine. This can be further modified by how the PCs interact later, but never more than 1 step in a single encounter, so an NPC won't typically go from Friendly to Hostile or vice versa in a single encounter.