I have no intention of attacking you personally. I'm a adult woman and I'm capable of criticism and I wish very much that I knew about everything. I don't want to write anything more about it except that you might read it yourself before posting it. All the best!
That's not true. You give a lot of misinformation. As an example with the house registration... both parents have to be present total nonsense. She can register with anyone who gives her permission.
It's not hopeless. Your mom can still get a birth certificate at the Australian Embassy for you. It is important that she has the 13 digit identification number, id card or house registry. If you can find that out then it's easy. I went through the same thing. Call the Embassy. Explain your situation. Tell them why it is important for you to get Thai citizenship. They will be happy to help you. If you have any questions... you can send me a pm.
I cannot speak for Australia but I think they are the same requirements.
I grew up in Europe and my children were born in Europe. We all have 2 citizenships and all 2 passports. It has only advantages and it is a mistake to choose one. It is even very difficult and sometimes impossible to get rid of the Thai citizenship.