Short answers, pulled from the story.
The definitive German Instrument of Surrender was signed on the 8th of May 1945 in Karlshorst, Berlin, at 22:43 local time. An earlier version had been signed at 02:41 on the 7th of May at SHAEF headquarters in Reims, France, but was not considered the final document.
Germany's cease-fire took effect at 23:01 Central European time on the 8th of May 1945, which corresponded to 00:01 on the 9th of May in Moscow time. Because the surrender entered into force on the 9th in local Soviet time, Russia and many former Soviet states have observed Victory Day on the 9th of May ever since.
Churchill addressed a crowd in Whitehall on the 8th of May 1945 with the words: "God bless you all. This is your victory. In our long history, we have never seen a greater day than this. Everyone, man or woman, has done their best." He then invited Ernest Bevin forward, who led the crowd in singing "For He's a Jolly Good Fellow".
Franklin D. Roosevelt died of a cerebral hemorrhage on the 12th of April 1945, less than a month before Germany's surrender. Truman, who succeeded him, dedicated the victory to Roosevelt's memory and kept American flags at half-staff for the remainder of the 30-day mourning period, saying his only wish was that Roosevelt had lived to witness the day.
Yes. Princess Elizabeth, the future Queen Elizabeth II, and her sister Princess Margaret were permitted to leave Buckingham Palace and wander incognito among the celebrating crowds in London on the 8th of May 1945.
Poland officially changed its observance to the 8th of May on the 24th of April 2015, when the Sejm adopted the Act on National Victory Day, establishing Narodowy Dzien Zwyciestwa on the 8th of May and abolishing the previous the 9th of May holiday. From 1945 until 2014, Poland had recognised the 9th of May in line with Russia.