"Indeed, we have heard much of your knowledge of the history of these wicked naga and their history and the Lady Lyubimov recommended that we seek you out immediately," a little flattery never hurt.

Spoiler
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Diplomacy (1d20+4)[9]
Bluff (1d20+2)[19] for the flattery

Do I have any idea what the skulls represent other than morbid decoration?

Knowledge (Nobility and Royalty) (1d20+6)[18] for heraldry
Knowledge (History) (1d20+10)[21]
Knowledge (Arcana) (1d20+14)[22]