This is what Nicholas wrote in his diary for his wedding:
"14 November - St Petersburg
The day of my wedding! Everyone had coffee together, and then went off to dress: I put on the Hussar uniform and at 11.30 drove with Misha [brother] to the Winter Palace. The whole Nevsky was lined with troops waiting for Mama to drive past with Alix. While she was being dressed in the Malachite hall, we all waited in the Arabian room. At ten to one the procession set off for the big church, from where I returned a married man! My best men were: Misha, Georgie, Kyril and Sergei. In the Malachite hall, we were presented with a huge silver swan from the family. After changing, Alix sat with me in a carriage harnessed in the Russian manner with a postilion, and we rode to the Kazan cathedral. There was so many people on the streets, it was almost impossible to pass!
On our arrival at the Anichkov we were met by a guard of honour. Mama was waiting for us in our rooms with the bread and salt. We sat the whole evening answering telegrams. We dined at 8 o'clock and went to bed early as she had a bad headache!"
So therefore Nicholas's best men were Grand Duke Mikhail (his brother); George, Prince of Greece; Kyril, Grand Duke Vladimir's son; Grand Duke Sergei Mikhailovich (Grand Duchess Xenia's brother-in-law).
Sorry I can't answer the second question. But I think Tsar Alexander III was Alexandra's god-father.