NSW Family provision and stepchildren

I know any answer will not be 100% guaranteed. But here is the question:

Can a Stepchild challenge a will of a step parent when they received a significant inheritance from their mothers estate? They have never lived under the same roof as the step parent, and the only financial benefit they have received was when their step parent paid for their travel to attend their mothers funeral (they were living overseas at the time). It was thought to be a loan, however it was never paid back or followed up for non-payment. The step parent is terminally ill (and was at the time of his wife's death) at that time he did feel that he had a moral obligation to leave a gift to the step child ( roughly 6 years ago) but now is thinking to remove this gift due to depletion of his estate.

Also I have been doing some reading, would a "considered persons" clause help in mitigating any legal proceedings?

There is no relationship either. Contact is maybe one text a year at most. He may see them if he drops his kids off to meet up with them or at an annual family get together. The relationship is cordial but distant - like an acquaintance.

Thankyou! could I ask is there a site where I can read up on some case examples such as what you have provided. The step parent concerned is my brother and he is finding this all very overwhelming. If I could read up on some examples it might help him gain some comfort and confidence in the decisions he now needs to make to ensure their kids receive adequate provision.