Best to go for the independent visa (189/190) if you have enough points, as 489 is a pain in the butt. Sorry. Only go for 489 if you do not have enough points.
You will not have Medicare on 489 (unless your country of origin has reciprocal agreement with Australia, like UK), so will need visitors' private health. Most people go with BUPA, for full comprehensive insurance (extras + hospital) you may be looking at paying about $200 a fortnight for 4 people. Please research this online, I cannot give exact figures. I pay $120 a fortnight for me and my son. this covers all extras and hospital with $500 excess.
You can get a job here, but please be prepared that it may not be in your field. Adelaide is a funny place like that. You have to be very lucky to get straight into your profession on arrival. Many people of good professions like doctors and engineers here work as UBER drivers, which is a bit sad, but it gets them a PR in the end!
No requirement for IELTS for main applicant for 887, but there is for a secondary applicant. Or you can use a university degree as a proof of English.
Adelaide is very livable in terms of rent and living expenses. There are some cheaper suburbs north and south, more expensive in the hills and near the ocean , you just have to look for there you want to be. You can rent a house or unit for your family for $300/week, if you want to start small. Plus other expenses: food, cars, energy bills, phones, internet. As an example, all my bills with rent average at $450-500 per week plus car fuel, food and mobile phone.
Yes, you can invite parents on 489.