My guess is, if they are offering you the personal interview after doing a phone and Skype interview, you are the guy they want - or at least one of a few candidates from their original pool. That's good! So, I would say this is more of a "get to know you" interview rather than one where they are assessing your technical capabilities as a pilot. So, as much as possible, try to fit in with their culture. Research the company and the flight department, ask good questions pertaining to their operations and the company's business. Show that you have done your research about THEIR operation, and that you want to be a part of it and will fit in. Be the guy that they want to spend 2 weeks on the road with. Friendly, competent, polite, but can have fun, has a sense of humor, and doesn't take himself too seriously. Also, despite your considerable experience, I'd guess they want to ensure you're flexible and humble enough to learn new things and to fit in with corp flying.
Because it's an interview, I'd still err toward the side of formality (suit and tie, shoes shined, all your documents in perfect order). Just sets the right tone - sounds like you did all that. If it settles into a friendly session after that, read the situation and lighten up accordingly. Always easier to dial down the formality as the situation eases up than to start off with "Hey dudes!" and realize they are all prim and proper.
Just thinking out loud, and all my opinion, so probably not worth much.
Good luck - sounds like a great opportunity.