# Pekah ... Remaliah

These are men's names. 

# conspired against him

"secretly planned to kill Pekahiah"

# Argob ... Arieh

These are men's names. 

# the citadel of the king's palace

"the fortified part of the king's palace" or "the safe place in the king's palace"

# became king in his place

"became king instead of Pekahiah"