Regarding newbies - here is my advice:
1) talk a lot before you go. Set their expectations. This is sailing - not the Four Seasons resort. Find out what they are interested in. Discuss their concerns. Talk about how they can help. Talk about spending time apart if desired.

2) start them on Bonine for seasickness the night before you fly down to the BVI. Slowly wean them down to half a dose and then nothing if they are feeling good after a few days.

3) If the weather is fresh, don't sail the boat too hard unless you are sure they are having as much fun as you.

4) Celebrate your time together. Cheers and have fun!