Since DMs don't read the DMG and, even if they do, they probably don't read or employ the social interaction rules (p. 244-245), it might be good to comment on what these rules tell us to do.
First, you set the NPC's starting attitude - friendly, indifferent, hostile. The NPC's attitude at the end of the conversation sets the limits as to what the NPC is going to be willing to do. DCs are provided in case what the PCs want has an uncertain outcome and a meaningful consequence for failure.
The PCs converse with the NPC. During this conversation, some PCs might be trying to influence the NPC's attitude to temporarily improve it. The DM meanwhile is portraying the NPC's agenda, ideal, bond, and flaw throughout the scene and presenting objections and other obstacles for the PCs to overcome as the conversation progresses. While some PCs do the talking, others might be trying to figure out the NPC's agenda, ideal, bond, or flaw so that it can be used to frame arguments in a way that is likely to get at the desired response. When the conversation has run its course, the PC's request, demand, or suggestion is judged by the DM and perhaps the dice.
So really, the best strategy here is to pay attention to how the DM is portraying the NPC and put your higher Charisma characters up to talk to the NPCs while higher Wisdom characters (or those trained in Insight) try to suss out agenda, ideal, bond, and flaw. Then use what you suss out to frame arguments so that you automatically succeed or have advantage on Charisma checks. Get the NPC's attitude to friendly or as close as you can, then make your request, demand, or suggestion. Spend Inspiration if you need advantage on the resulting check, if there is one.
As I noted upthread, the Baron - unlike a lot of other NPCs in the module - has no ideal, bond, or flaw listed. But it can be derived from the information in the book. I would write those up accordingly and run this social interaction challenge with this structure in place. Maybe the players have to roll some dice and maybe they don't, depending on what they do, as with all other actions they may take in the game.