I believe the two elderly brothers were raised in the traditional FLDS faith. I've researched this family including the children and Nauvoo, IL is a common theme in their religious faith. Nauvoo is where Joseph Smith left after being kicked out of Missouri.
The following explains Warren Jeffs/FLDS ultimate goal to returning to Missouri.
Like all the FLDS prophets before him, Warren Jeffs routinely taught his followers that the church would some day relocate to Jackson County, Missouri, the place where Mormon founder Joseph Smith tried and failed to establish Zion in the 1830s.
Facing an extermination order from Missouri Governor Lilburn W. Boggs, and following several bloody attacks by the Missouri Militia in 1839, Joseph Smith led his followers out of the state and took them to Nauvoo, Illinois. Developments there eventually led to Smiths 1844 assassination in nearby Carthage, Illinois.
Since that day, many Mormon faithful, including several fundamentalist sects like the FLDS, have believed that the church would someday return to Missouri where Smiths Zion would be rebuilt.
As recently as the annual FLDS conference, held April 6, 2002, in Colorado City, AZ, Warren Jeffs spoke on behalf of his ailing father, Rulon Jeffs, and told the church faithful that Zion was to be reestablished in Missouri. His plans apparently changed shortly after the death of his father five months later. By November of 2003 the YFZ Land corporation had been formed and property was being acquired here in Schleicher County.