Hi @Beth1 - Thanks for reaching out! This is such a fun area to get to explore in a van. There are seemingly endless options to choose from, but having traversed that area a fair amount myself, I'd love to share some highlights and suggestions:
With so many people choosing camping vacations this year, campsites are becoming fully-booked faster than normal, especially with spacing/cleaning policies and making sure to follow all local travel guidelines. Most of the town's websites linked above have suggestions for campsites. Hipcamp is another great resource for finding neat spots. We suggest starting with campsites and seeing what is available, and then picking hikes/activities based on what's nearby!
Hopefully this is a good start of things to look into. We'd love to stay updated on the route you end up choosing. Don't hesitate to ask if you have any more questions!
The Four Corners area, within the Navajo Nation, is one of my favorite areas in all the world. Looking at current conditions, I learned that Navajo National monument is closed, Canyon de Chelly national Monument is closed, and Monument Valley Tribal Park is closed. Covid 19 has hit the Navajo Nation very hard, although it doesn't get much mention in the media.
The situation may improve by summer, but pay attention. The fall is the best time to roam around the Four Corners anyway, in my opinion.
When you do get there, I would recommend Canyon de Chelly heartily. Abundant Pueblo ruins, wonderful canyon scenery, fabulous rock art, together with contemporary Naavajo society. dee Chelly is unique among NPS areas in that it is part of the Navajo Nation as well as an NPS area, so people are living, herding, and farming within the Monument. It gives a vibrancy to the area that is unique. To really experience the area, hire a Navajo guide.
Monument Valley would be a national Park except the Navajo got there first. The classical western movie "Stagecoach" was filmed there and brought the area to prominence.
Navajo National Monument preserves and protects the most outstanding cliff dwelling found anywhere, Keet Seel. Incredibly well preserved, it is a 17 mile hike. Betatakin ruin, closer to HQ, is a shorter trip.
You will be visiting Indian country. In some ways, like going abroad. You have the Navajo Nation, largest Native American group in the USA, surrounding the Hopi Reservation, descendant of Ancestral Puebloan groups who left us all those National Monuments. They have a long history of conflict.
Expect different behaviors and customs. Be flexible and adjust. Don't be the Ugly American. Exposure to contemporary Anglo society varies widely. You could meet a Navajo with a university graduate degree who grandparents speak only a bit of English.
This is just the tip of the icerberg. It is fascinating land - wild, scenic, exotic - worth many trips.
Hopefully the situation will improve by summer