Hi, It's so hard to say what a family would spend a month because everyone spends differently. The most significant cost will be housing - I assume you'll be renting so that cost will depend where you're working and how far away from work you want to be, the size of the property etc.
I recently did some calculations and I feel a family needs a household income of about $AUD120,000 to survive in Sydney. Included in that I calculated running a car, a few extracurricular activities for children etc. I'm sure many families manage on less but probably live further away from work and rely on public transport. This figure includes health insurance for the immediate family but I think the cost of your parents health requirements could be a lot.
All the best with your plans.