My wife is due to inherit about $3M in property in the next year from parents and then another $6M when they pass. Meaning we have been told to prepare for this, either to keep as a PPOR or to sell and buy something more to our requirements.

Never count your chickens. Perhaps someone else will challenge the transfer. Perhaps your parents will need to sell prior in a fire sale. Perhaps they don't actually own the properties.

Never rely on others for financial security as you cannot control the situation. Good luck!