Past continuous vs. Past perfect

Question

It's a story that happened in the past at an airport. It starts this way

When I got to the check-in desk my parents were nowhere in sight. I was waiting for them until it suddenly occurred to me that they had already checked in and they were waiting for me in the departure lounge. This was a real problem because I had given my passport to my mother so I couldn't check in.

I immediately called my parents on their cell phone. I was right they had already gone through to the departure lounge. They were waiting for me for almost half an hour at the gate.

I think for 2nd and 3rd one we can use past perfect continuous cause we are talking about length. But I have doubts in these three bold part.

Answer 1

"Until" is a word that only makes sense when something is going on at the time the change in action described by "until" happens.

Past Tense: "I worked until the sun set."

Present Tense: "I am painting until you tell me to stop."

Future Tense: "I will drive until I get tired."

The past perfect tense means something happened in the past and was completed. So it's inappropriate to use with "until." You need to use the past continuous tense because something started in the past must still be going on.

Therefore, your fist bold example using the perfect continuous tense is correct.

Your second bold example is also correct. It is using the past continuous tense to describe an action started in the past and still continuing. (Compare this to "...they had already checked in...", which is the past perfect case because the past action was completed).

Your third bold example is not correct because the past action was completed. It should use the past perfect tense. "They had been waiting..." (Although, it would read more smoothly to say, "They had waited at the gate for half an hour.")

Answer 2

There's nothing incorrect or ungrammatical in your writing--at least in Standard American English.

In British English, there is often a stronger expectation to use the perfect aspects in contexts where there is an open choice for Americans.

Whether your choices are the best in terms of style is another question.

Here is just one alternative that I think would help a reader process the story more smoothly:

When I got to the check-in desk my parents were nowhere in sight. I waited for them until it suddenly occurred to me that they might have already checked in and were waiting for me in the departure lounge. This would have been a real problem because I had given my passport to my mother so I wouldn't have been able to check in.

I immediately called my parents on their cell phone. I was right. They had already gone through to the departure lounge. They had waited for me for almost half an hour at the gate.