Short answers, pulled from the story.
The Loyal War Governors Conference convened at the Logan House Hotel in Altoona, Pennsylvania on September 24 and 25, 1862. Thirteen governors of Union states gathered to discuss the war effort and state troop quotas.
Altoona became that location due to its proximity to Midwest states and New England. The city offered excellent transportation through the massive Pennsylvania Railroad center based there.
The Battle of Antietam on the 17th of September 1862 allowed Lincoln to claim the victory he so desperately needed. He issued the Preliminary Emancipation Proclamation on September 22 following this key event which became a main topic among the governors.
A total of twelve signatures were included on the address presented to the president after Governor Austin Blair of Michigan arrived late but joined fellow delegates going to Washington D.C. the same day. Executives of Vermont, Connecticut, Kansas, Minnesota, and Oregon gave approval of document while those of New York, New Jersey, Delaware, Kentucky, and Missouri declined it.
Because meeting in Altoona occurred, Lincoln able to issue document with new sense authority delivered by northern governors and victory at Antietam. The Emancipation Proclamation legally freed slaves in seceded states and parts of states not under Union control.