Who were the royal families relations in Europe in 1914?

Answer 1

The fact that George V, Tsar Nicholas II, and Kaiser Wilhelm II were all cousins give you an idea of how closely inter-related the royal families of Europe were in 1914. As a result of all the major monarchs at the time essentially being part of one big extended family (through their relation to the House of Saxe-Coburg) many people in the lead up to WWI thought that war between the major powers would be prevented by their diplomatic intervention.

There's information on the relevant dynasties here: the British royal family was at the time (and still is) part of the Saxe-Coburg family, which is descended from the House of Wettin. There is information on these families in the links below, and a good description of the diplomatic activities of the Saxe-Coburg monarchs all over Europe can be found in Niall Ferguson's book 'The War of the World'.