What is the required number of witnesses to prove the crime of adultery if two men and two women commit adultery in one room, or two men with one woman in one room? Are four or eight witnesses required?

Four witnesses are sufficient to testify against these individuals. They testify against all of them, and it is not necessary for those who testified against two of them to be different from those who testify against the others. This is because the eligibility of witnesses is not invalidated by performing testimony, and as long as the eligibility remains, the testimony is accepted.