From the Adventure Notes, which I've fleshed out a bit:
This is your first social encounter (with some exploration by way of Int checks):
A DC 15 Insight check reveals the High Priest wants to help the PCs in their quest but is holding back on resources (in actual fact he is holding back potions of healing, in case the PCs fail, and to help the Townsfolk out should the Demon get free)
A DC 20 Persuasion check if the PCs ask for assistance, convinces the Cleric to provide the PCs with 10 healing potions for the quest. Grant advantage to anyone who made the Insight check above. PCs can also Intimidate him at the same DC, but risk falling out of favor with the Church (and angering Bob the PC Cleric) in the process.
A DC 15 History check reveals that Bargle is famous in the area as an evil-doer and powerful mage who is wanted by the local authorities, with a hefty bounty on his head (5,000gp).
A DC 15 Arcana check (by a PC who succeeds on the History check) reveals he is a failed archmage (and capable of casting 7th level spells!)
Leaving aside skill checks, is there anything you can do with your magic here?
Otherwise, I would be most inclined to say you pass both Int checks (History and Arcana) providing the PCs with the relevant Lore and info on Bargle. You likely fail the Insight (+0) and Persuasion or Intimidate checks (+3/+0) with the party 'Face' being better here.