(Solution) Difficulty composing in Sicilian music style

I’m no expert, but a guitar is not a traditional Italian instrument and you’re more likely to be invoking Spain. I do know that you’re much more likely to find something resembling a 4-course ukulele, so Guareschi’s Charango might be worth checking out (5-course, and whether the courses are tuned the same I don’t know, but given the reference number I’m not sure he’ll pick that up! That said, give me a nice Alicant or Duvanera with some Arancini and it won’t be long before I’m shouting out something a bit more Sicilian than that!), and that small Psalter and Harp-like instruments are the other plucked strings common in that idiom.
Oddly enough (at least I thought so when I first discovered it, and to be honest I still think so), the jaw harp was probably the most widely used instrument in the southern Italian islands at that time. If he’s interested in credibility, you should use one of those. I don’t know where you can get a deeply sampled example of one of those, especially if you need convincing legato and second jaw harps!
Small recorder-like instruments were also common, and they had bagpipes, which, based purely on visuals, I suspect had more in common with Northhumbrian and Uilleiann pipes. Xtant Audio has Uilleann pipes, but I’m not sure you can sell that sound as traditional Scicilian to most people these days.
I found this site, which gives you insight into what Sicilians consider the instruments of their heritage. But does he want 18th/19th century Sicily or Hollywood? “Well, it sounds a bit foreign, but that’s fine!”