Annas and Caiaphas

Who was the high priest that year?
"Caiaphas" (John 18:13).

To whom was Jesus taken first?
"Annas" (John 18:13).

Who was Annas?
Caiaphas’ "father-in-law" (John 18:13).

Why would Jesus be taken first to the father-in-law of the high priest?
Annas, also identified as "Ananus" or "Ananias" in secular history, had been the high priest since 7 AD but the Romans found him hard to push around so deposed him in 14 AD. For the next several decades, Annas was the puppet master who engineered the Romans to appoint as high priest his puppets, including five of his six sons, as well as his son-in-law Caiaphas. Caiaphas was the official high priest from 18 AD to 36 AD, including "that year" (John 18:13), which was about 33 AD, but the one pulling the strings remained Annas, whom the Jews considered the real high priest, whom Judaism appointed for life. (This Annas should not be confused with the last of his five sons who served as the official high priest in 63 AD, was also named Annas, and known as "Annas the son of Annas.")

When did Caiaphas advise "the Jews that it was expedient that one man should die for the people" (John 18:14)?
See Caiaphas.

Who was the “another disciple” (John 18:15)?
John, the writer on this gospel, who also called himself the "disciple whom Jesus loved” (John 20:2).

Where did they go?
"Having arrested Him, they led Him and brought Him into the high priest’s house. But Peter followed at a distance" (Luke 22:54).

To the house of which high priest - Annas or Caiaphas?
While the Bible mentions the presence of both Annas and Caiaphas in this house, it does not specify who owns it. However, it is likely to be Annas' for two reasons: First, Annas, who controlled the sale of the animals for sacrifice at the temple, the currency exchange for buying those animals, and the temple tax, was one of the richest men in Jerusalem and the one wealthy enough to own a house, built around a "courtyard" (John 18:15), with at least one hall that was large enough to gather Israel's religious leaders and hold a trial (see below). Second, the Jewish historian Josephus mentioned the house of only Annas and in the same breath as the palaces of the Herodian royals, Agrippa and Bernice:  "The others then set fire to the house of Ananias [Annas] the high priest, and to the palaces of Agrippa and Bernice" (The War of the Jews, 2.426). If it was Annas' house, Caiaphas either lived there with his wife - Annas' daughter - or was there to conduct the informal trial of Jesus.