Bible Study Seattle

How is it that a person becomes part of Jesus’ priesthood?  The Aaronic priesthood was composed of Aaron and his sons and their descendants.  It appears that Jesus’ priesthood, or the Melchizedek priesthood started with the selection of Jesus as high priest, and the twelve apostles as under priests.  From there, the great commission netted many more priests.  Many think the total will eventually number 144,000, some think more.  What role does the next life have regarding priesthood?  Will the priests be involved in killing the wicked?