Traveling with your Husband/wife/significant other/domestic partner/whoever it may be is hard enough, and generally, you share the same interests, or at least know what they like (or don't). And really, the person in charge of planning usually calls the shots. So planning a trip that involves three generations of family, extremely varied interests, and even different days off of work, takes a lot of work and so much organization!
So how does one stay organized, while still letting everyone traveling know what the plan is? Anal retentive itineraries. I'm serious. I am so particular about travel info, and sharing with everyone, that you could literally get lost all alone and have no problem figuring out where to go. And they are done in such a fashion that both my 25 year old brother and 87 year old grandma have to issues figuring out exactly what I mean.
The first thing I do is make an itinerary calendar in Microsoft Word. I make sure the times have the time zones, the hotels have the confirmation numbers, and flights have the flight numbers.
And because I'm so OCD (and not because I don't trust everyone else) I then break it down day, with bullet points to highlight each activity. At the end, I add some tips and tricks for traveling. I always see a mistake as a chance to learn, and yes, most of my tips are based on experiences I've had in the past.
So if you want everyone to be on the same page, just make an itinerary. I promise, it will keep you from losing your travel group. And from killing them.