My advice is to think about and plan what you might do in whichever of the destinations you decide on (they are all beautiful) and pair it back by between 1/3 and 1/2. Many people when they try to see everything don't get to spend enough time to take in the beauty and magnificent area they are in. They end up exhausted and partially frustrated.
Many of the nature types of things you may have to be in an area a while to have a chance in seeing some of the wildlife.
Research the weather carefully for the timeframe you are considering visiting. At higher elevations, it can be much colder than you expect in the summer time and in the spring and fall, snow is not unusual.
If you decide to go with one vehicle, erase the expectation of privacy unless you are talking about when you and your's may take a walk or do something separate from the other couple. 4 adults and 2 children in a 40' or less RV/Camper leaves little unused space. Might even want to spend a long weekend at a 2 bedroom Airbnb with this other family just to see how well you all love spending time together in close proximity.
Best of luck and hopefully the answers you get are raising more questions for you to ask. It's a great community here to offer advice.
