Different consecutive (therefore) and causative (because) conjunctions
他很累，从而晚上9点就上床了。

从而 means &quot;since then/after that&quot; - '他很累' is not a specific event, therefore the sentence is not grammatical

既然他很累，就晚上9点就上床了。

wrong final particle, it should be &quot;既然他很累，就晚上9点就上床吧!&quot;

他晚上9点就上床了, 因而他很累。
He went to bed at just(就) nine O'clock, therefore (因而) he is very tired

Why would he went to bed as early as 9:00PM caused him to be tired?
Also, you don't need to use the pronoun 他 twice in the same sentence.
A better example:

&quot;他每晚9点就上床, 因而从未看过十点播放的新闻。&quot; -- &quot;He goes to bed at 9 o'clock every night, so he has never seen the news broadcast at 10 o'clock.&quot;

因而 is an independent conjunction . As long as there's a clause stating a reason, you can use  因而 to connect it to the clause stating the result, For example: &quot;他家中没有电视, 因而从未看过十点播放的新闻&quot;