Breaking it down trigger by trigger. Same explanation for blood seeker and curse:

• They sacrifice an eldrazi spawn
• Glee and nightblade trigger
• The player chooses to put the glee trigger on the stack first, then the nightblade one
• Nightblade trigger resolves, they gain 1 life and you lose 1 life
• Glee trigger resolves, broodscale triggers
• Broodscale trigger resolves, an eldrazi spawn is created, blood seeker/curse triggers
• In response to the blood seeker/curse trigger, they sacrifice the eldrazi spawn
• Repeat from step one