Unfortunately I can’t upvote this more than once. Also, if only I could force people to follow this advice.

Ditto.

Look in any English language dictionary. Show me an entry that states a couple is more than two

I‘ll wait.

Wrong. A couple is two exactly. After the wedding: Oh look at the happy couple. There aren’t 3 or 4 people standing there, 2 people are standing there. A couple.

To couple train carriages together means to attach two carriages together. There are more carriages behind that one, but they were all individually coupled together.