Another thing if you want to buy more time is to request and buy any extension which you won't be eligible for and you will get a 7-Day extension denied stamp giving you 7 days from the date of application to leave the country.
You can only get dependant status from the main holder of the OA Visa. Suggest you join Thai Visa Advice - Q&A and ask your question for expert answers.
the OP stated that he already provided a proposed date and now they're asking for tickets, he was asking if his tickets have to be the exact same as the proposed date.
The application asked for a proposed flight date and number, you're under no obligation to show tickets for that proposed date, you can change your mind or dates.
you can also view a summary of all the information that's going to be entered before you submit it (minus the supporting documents), I suggest you screenshot every part of that long summary. Triple check everything