From what I understand, the Inquisition mainly used torture as a means to gain a confession out of those in their care, before ultimately executing them. For converting people, they usually used the fear that sparks from their name to do all the dirty work, but when that doesn't happen, do they result to torture?
How were they created, and why was it the Spaniards that created the organisation?
Have any of their members start having doubts about this being their gods' will, or somewhere along the line, and end up being on the receiving end of one of their colleagues' sessions? Were they dissolved because they took their witch hunts a bit too far by accusing someone high up, or were torturing/interrogating someone with a high rank in the monarchy?
The question is a good one, but it reveals more about the myth of the inquisition than the workings of the institution.
First, the inquisition was a fully fledged legal system. In fact some scholars have argued that it is the first modern, codified court system in Europe. Unlike almost every other court of the time, every aspect of the Inquisition's operation was written down in its charter.
Second, within the framework of the time (which is decidedly not modern) torture was not punishment. Torture going back to Roman jurisprudence was a valid tool for determining the veracity of statements. In some cases, particularly that of slaves providing testimony on behalf of their owners, it was the only recognized means of determining if claims were true. As with other aspects of its procedure the inquisition had rules governing when torture could be used, as well as how much and what kind of torture would be used. In general, it was only used when the defendant's testimony was inconsistent internally and/or not well corroborated by other witnesses. Often, torture was not required because the evidence of guilt or innocence was clear enough that torture was not needed to verify claims.
Third, the Inquisition had no role in converting people. The Inquisition only had jurisdiction over baptized Christians. The individuals it was first designed to investigate were conversos (formerly Jewish converts). As baptized Christians they were subject to the Inquisition and if they relapsed into Jewish practices they were guilty of heresy. Yet, even in those cases the Inquisition was not interested in converting them, as they had already converted.
I would suggest reading Kamen's Spanish Inquisition or Netanyahu's Origin of the Spanish Inquisition