2 Comments Wills, probate, letters of administration, powers of attorney
Your step-siblings and you as one of the biological children are entitled to inherit your father's assets. In case that he will pass away and you will not be included in the will, you can contest a will if you want. You can view https://orglaw.com.au/defining-who-is-a-child/ to know about who are eligible to contest a will. I'm not an expert, I just share what I read.
The best possible scenario is that your father writes a will or updates his old will after the separation. If there is no will, you as the biological child and your sister are entitled to his estate, as well as his new partner and any siblings/parents still alive. You and your sister will be the first to be looked at because you are his biological children. If your father does not remarry and does not divorce your mother, she too will be named as a possible beneficiary because technically she is still his legal wife. You can contest a will but keep in mind, like any court case, you will need legal representation and this can be costly and the legal process can take quite a lot of time. Sometimes the cost is more than the estate itself. The best possible scenario, since your father is still alive, is for him to have a current will. After he passes, you should really consult a legal professional on what the best option is for you and your sister.