TIP #1.
Try and capture the moment by using a sense of humor. Did you accidentally cut off mom's head in teh photos? Well, if she has a margarita in her hand... that's funny! Remember- family vacation photos serve one purpose- to remind you of great memories.
TIP #2.
Here's a trick I learned while working in TV. The best photos are when light is on the face of the subject, but the problem is that most of us squint when the sun is in our eyes. Try this: close your eyes, and while doing so, stare at the sun for 10 seconds. DO NOT OPEN YOUR EYES DURING THIS TIME!! When the photo is ready to be taken, look away from the sun and into the camera lens. Like magic, you won't squint, since your eyes have now adjusted to the light.