Thanks guys for taking the time to read and provide valuable advises, really appreciate the effort! I rang immigration on this issue this morning, below are the instructions from them
489 holder expecting a baby in Australia will need to complete Form 1022, mail to Brisbane office and will be advised a process fee of AUD 900
489 holder expecting a baby outside Australia will have to submit Application for Provisional Skilled Regional - Subsequent Entrant Visa (489) after baby in born and a fee of AUD 3600
887 is a pathway from 489, it means that you will need to be a holder before you are eligible to apply for 887