"So that" and "in order that" have the same meaning and are used in the same way. They both are subordinating conjunctions that express purpose, and are always followed by a subject and a verb.

"In order that" is a subordinating conjunction. It links a dependent clause to an independent clause.

"So that" is a subordinating conjunction. It introduces a dependent clause and joins it to a main clause.

You don't need to repeat the subject after "but" if both parts of your sentence (clauses) have the same subject. Therefore, you can mention it again or omit it in the second clause.

Because must be followed by a subject and a verb. Therefore, if the subject of both clauses is the same, we have to repeat the subject or the subject pronoun after "because".