where引导状语从句和名词性从句的区别

where引导状语从句和名词性从句的区别
where引导状语从句，主句和从句中的不及物动词后面还需要加介词嘛，是I live where they live.还是I live in where they live in.
where引导名词性从句，从句中不及物动词后面还需要加介词嘛，是That is where their happiness springs from.还是That is where their happiness springs.
为什么？