I pick number 3. The creation of West Virginia was Constitutional because the Virginia legislature that remained loyal to the Union, and which was recognized by Congress voted to create it.
On April 17, 1861, the Virginia Secession Commission voted to submit a secession bill to the people. When this was approved, the delegates from the western counties marched out of the Secession Convention, vowing to form a state government loyal to the Union. These delegates gathered in Clarksburg on April 22, calling for a pro-Union convention, which met in Wheeling from May 13 to 15. On May 23, Virginia voters approved the Ordinance of Secession.
Following the Union victory at the Battle of Philippi, a Second Wheeling Convention met between June 11 and June 25, 1861. Delegates formed the Restored, or Reorganized, Government of Virginia, and chose Francis H. Pierpont as governor. Congress recognized the Restored Government as the legitimate government of Virginia. John Carlile and Waitman T. Willey became United States Senators and Jacob B. Blair, William G. Brown, and Kellian V. Whaley became Congressmen representing pro-Union Virginia.
On October 24, 1861, residents of thirty-nine counties in western Virginia approved the formation of a new Unionist state. At the Constitutional Convention in Wheeling, which met from November 1861 to February 1862, delegates selected fifty counties for inclusion in the new state of West Virginia. Some of the counties that did not support statehood were included for political, economic, and military purposes. One of the more controversial decisions involved the Eastern Panhandle counties, which supported the Confederacy. The Baltimore and Ohio Railroad, which ran through the Eastern Panhandle, was extremely important for the economy and troop movements. Inclusion of these counties removed all of the railroad from the Confederacy.
Since the Restored Government was considered the legal government of Virginia, it granted permission to itself on May 13, 1862, to form the state of West Virginia and the requirements of Article IV, Section 3 were met.
The United States Senate on July 14, 1862, approved statehood for West Virginia. On December 10, 1862, the House of Representatives passed the enabling act as well and on December 31, President Lincoln signed the bill into law, approving the creation of West Virginia as a state loyal to the Union. On March 26, 1863, the citizens of the fifty counties approved the statehood bill and on June 20, the state of West Virginia was officially created.
You can complain about the process all you want but the Supreme Court also granted de facto recognition of the Constitutionality when it agreed to hear the case of Virginia v West Virginia in 1871.
Another interesting point regarding Virginia secession that I just noticed: Their ordinance of secession was issued on April 17, 1861, its text requiring that it be ratified by a general election which was held on May 23. However, it was admitted to the Confederacy on May 7, and CSA troops were already in Virginia before the state's citizens had ratified secession.
Nope. Had that been the case, they would have been the government of the Unionist state of Virginia, USA, rather than a newly-formed state.
Francis H. Pierpont, the Unionist Governor of Virginia, remained Governor of Virginai for three years after the end of the Civil War.