Can we travel carrying old and new passports while waiting for processing of form 929?

I submitted the form and it says it will take 4 weeks to process.

This is for my parents visa class 600 (3 years multiple entry) Problem is I want to book tickets and don't want to loose money if it doesn't get processed on time for any reason.

I read comments some people travelled with their old passport and staff updated it. Is it risky to do?

Is there any way we can make this process faster? By calling them or something?

marked as duplicate by k2moo4, Mark Mayo May 22 at 0:10

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.