We will be coming down from Tortola to pick up guests at the airport and dropping them again a week later.
What's the most convenient way of doing it ?
thanks

I am assuming you are coming by boat.
The process is something like this.
Clear your vessel out of the BVI and check in to US C&I - can be done in Cruz Bay STJ or in Charlotte Amalie STT.
The absolute shortest boat trip on your part is to pick up a mooring off Cruz Bay STJ and have your guests take a taxi to the ferry from the airport and then pick them up when they land in STJ.
If you want to take your vessel all the way down to Charlotte Amalie you could anchor right by the airport in Lindberg Bay and pick them up by dinghy or get a slip at Crown Bay and have them meet you there. There are a few other anchoring options but none closer.
After they are on board you can proceed back to the BVI and clear in with their names on the manifest.
If you must drop them off in the USVI at the end of the week you must again clear out of the BVI and into the USVI - once again dropping them in Cruz bay STJ is the easiest and shortest trip for your vessel but the other info is about the same depending on how close you want to drop them to the airport.

Most convenient for you is to have them take the ferry to West End and pick them up there. Otherwise, I like LocalSailor's Cruz Bay approach. We dropped crew in Cruz Bay in January and it worked nicely.

Cheers, RickG

is a few hours a of sailing a bad thing? Crown Bay is a great stop to laundry, reprovision, and top off water.

We had a last minute situation last Feb. My daughters flight down got screwed up so I arranged to have Kevin Campbell meet her at STT in the PM and take her to Red Hook while we cleared out of the BVI's in the AM. Moored at Caneel, dinked in, cleared in and headed to the ferry dock. Perfect timing next ferry had her on it. Just get the customs and a blank immigration form for the new crew B4 leaving the BVI's.

No argument there from me - underway is my favorite way. Leaving Crown Bay headed to the BVI, an overnight in Christmas Cove or along the N. Shore of STJ would be a wonderful peaceful welcome to any visitor <img src="http://www.traveltalkonline.com/forums/images/graemlins/Thumbsup.gif" alt="" />

Just my opinion, if I was planning on staying in the BVI I'd meet them at West End (Rick's first suggestion above). That advice might change depending on cruising grounds, how late they arrive...