Lots of missing info David, but with kids and a dog, you'll all be happier if you can take the attitude "the vacation is where we are" and don't make it a "forced march". DO NOT set a rigid schedule, and do not make non-flexible reservations. Long days of extended motoring in hazy-hot-humid weather or getting stranded in an extended period of rain (in a place with no shore activities) will not make for a happy crew.

If you can be flexible to vary your length and direction of travel each day, and set your stops based on weather and sailing conditions it will be a much better time for all.

So assuming you have a limited vacation time slot of a few weeks and if you have a destination in mind, my best suggestion is to "deliver" the boat to a point within about 50 miles of your destination without the entire family, and have your wife travel by land to meet you when it's time to bring them along. If you need to deliver the boat during weekends, you could leave the boat at intermediate stops during the week.

With "the vacation is where we are" as your #1 agenda you can vary direction of travel and distance and do more pleasure sailing and/or various other activities too, while on vacation.

As for planning speed -- of course that depends on your boat and you. I use "the slowest VMG I will sail before firing up the engine" as my planning speed and that varies according to many factors.