Become familiar with the various modes and controls, if you have enough time, learn them until intimately familiar. Best learned in a quiet setting, practiced in one with distractions (just like there will be on your trip).
For instant soft, even light, position your subject(s) in the shade.
In outdoors, contrasty situations, position yourself about ten feet from the subject(s) and turn on the flash. This will help reduce the contrast.
The documentation of your trip is basically the telling of your story as a family sharing a journey. Do not be stingy with your photography. Take several times the number of pictures you think will be needed. Why? Because each journey unfolds in its own way, but you do not know what that will be, so you make enough photographs so you have a multiplicity of potential paths when you edit your pictures. Yes, EDIT. Resist the urge to put up all 4,000 images on Flickr etc. No one wants to see all of them, plus they will tell a jumbled story.
Start before the trip. Photos of the planning, things like training (physical, etc). How you get there (car, train, ship, plane, bicycles, etc.). Your arrival, wht time was it, first impressions, did you meet up with family or friends? Eat? Take pictures of signs denoting your location, and place family around them. As the saint said, "All the way to Heaven is Heaven". It is not just about the destination, but all the way there. Resist getting caught in the Flickr/Instagram/FB cliche's, like photographing the food at breakfast. After your trip, you'll wish you'd gotten your family.
It's not about the spectacular, though you should get those shots too. The playful moments, and the quiet ones too. The SO snoozing in a hammock or sofa, the kids worn out, the in-between moments. Everything matters.
To do this well, be prepared. Have your gear ready, batteries charged, spares along with you, but most of all, be mentally prepared. Take portraits, posed and candid. Your family will get used to you snapping, but be sure to not interfere with the flow of life. Instead, immerse yourself in it. Photography should be a integral part of the experience, not outside of it.
Be certain to photograph the members of your family as individuals and as a group. Resist the urge to become a director, telling people to do this or that, or do it again. Save that for a few formal moments per day Be a photojournalist, fluid, fast, and anticipating gestures, prepositioning yourself for your own preferred point of view. Be sure to take close-ups and overall shots showing plenty of context. If you have any doubts, overshoot, but learn to be fast and stay in the moment. Always remember to participate while photographing.
One accessory I recommend, which is inexpensive but crucial is the smallest table tripod that will hold your camera. Like the one pictured here. Why? So you can use the self-timer and the photographer can be in the picture, too.
Take an AV cable, so you can do slide shows of your pics at night in the m/hotel.
Share the photography. Encourage each family member to use their phones (of own cameras). They will get things you missed, and have their own individual way of seeing.
This will sound retro, but...when you get back, as soon as possible, edit all the pictures (be thorough) and make prints. Yes, prints. Try Mpix, or any of several services. Run 10 files through to see if you like how they look, the paper etc, before sending the big batch.
Now, make an album(s). Hard drives crash, data, like the people that create it, go corrupt. Paper is the ultimate back-up. There is no end to scrapbook ideas on the web. I'll regret this, but Martha Stewart has a great idea with this: [Link]. For albums, KOLO [Link]. Top quality, archival paper, well-designed and just elegant.
Most of all, enjoy your trip. Be in the moment, shoot on the fly. Your journey and family matter most.
If anyone has any questions, please comment or e-mail me.