You don’t have to register the TM30 within 24 hours of your visit to immigration. You have to register it within 24 hours after you arrive where you’re staying. So, if you’re staying in the area covered by the immigration office you’ll be using, they will want to see a TM30, and you have one, so you’re good.
You might also explore the possibility of confirming your daughter’s Thai nationality, assuming of course that she’s also your wife’s daughter 😊. That will make things easier for all of you.
As things currently stand, you will need to show a flight out of Thailand on, or before, the date you will get stamped in for in order to get the CoE (without which you will not get on the plane). Now, if you're going to stay longer than that then you have a couple of options; Buy a flexible ticket where you can change the return date easily. Buy a 'throwaway' ticket out of Thailand on the date needed and then buy your return when you know your return date.