Well, at least you've got the Sydney bit right but a few misunderstandings on the rest.

By " I'm coming from Croatia, Southern Europe, and I feel I doesn't belong there at all, no life I'm expecting, rude people, knowledge is not appreciated, you can't find a job and bad (poor also) country and schooling systems. "

If that's what you are thinking Australia could be about, whilst I can understand any new immigrant having reservations about moving to a new country on the other side of the planet, I do not think you have to feel it will be as bad as what you envisage and in being a student you'll likely find that assimilation may happen easily enough - a lot is to do with having a good attitude.
Australia is a lot larger than Croatia and in fact all of western Europe will fit within Australia, Sydney a city of something about 5 million people and though you'll find Australian cities somewhat different to Croatia in that we do not have the older buildings and history, towns and villages often more compact whereas Sydney extends from a city centre out to a huge urban sprawl and then to ajacent rural areas with towns part of that, it is not to say there is no life but likely a different lifestyle to be experienced.

You can get some rude people in just about any country and it would be wrong to say Australia does not have some and we have even had some isolated issues where there has been violence against people but Australia has people originating from over 200 different nations and generally the Australian people are of a peaceful friendly nature, not rude at all.

By knowledge not being appreciated, I'm not really too sure what you mean by that but in terms of general knowledge you may find that some people are interested in what knowledge you have of Croatia and Europe in general for a lot of Australians are interested in travel and Europe in general; and educational knowledge is usually a prerequisite to getting good employment, education being valued and you'll find that our education facilities are very good - several hundred thousand overseas students come to Australia each year and so that may say something.

As to getting work, that is not always an automatic result of having been to a high school and then on to a college or University and just as I suspect you would find employment in many European countries as being competitive, it is no different in Australia and all countries are likely to have difficult times in coming years with higher unemployment because of the global economic situation - you may want to read up on The Great Depression!

To answer some of your questions more specifically.
. Life in Sydney can be as varied as you like to the extent of affording it but Australia in general has a much milder climate than what you'll be experienced to and so lifestyles are geared much more to the outdoors, country and of course many great beaches for various watersports.

. Our schooling here is Primary for six and High Schools for up to six also to be eligible for University courses, and you have primarily public schools of the largest %, and then some Church schools and Private schools for which there are higher fees than public schools.
No Aviation high school and if you mean by aviation you want to becomer a pilot, you'll find various flying schools where you start off getting a private pilots licence, moving on to a commercial licence and then a senior commercial licence for either fixed wing or helicopter and various endorsements for multi engine, instrument ratings and different aircraft.

Working as a pilot can be as diverse as becoming an instructor, flying for small charter companies or smaller companies doing a mixture of charter and tourism work and a lot of pilots will do that kind of work to gain hours of experience before they may have an opportunity to apply to larger airlines.
Other airline pilots may be ex-airforce pilots and getting into the airforce is something different again.

If you are thinking of aviation engineering or trades there are various university courses or apprenticeships either privately or with airforce training that can lead to such careers.
To get a fuller picture of all that you may want to google flying schools, RAAF, Aviation courses, TAFE etc. and see what you find just as googling Sydney and NSW will also give you a wealth of knowledge before the family move.

. Seasons are opposite that in Europe - think northern hemisphere Vs Southern
. 5&6, yes, . 7 already answered.
. 8 we have crime but not a lot and illegal to be carrying guns here unless you have a licence and are going hunting or to a shooting club, likewise also illegal to carry knifes regarded as weapons, even in some states [yes NSW] a clasp knife like a Swiss Army one.
.9 Our police forces have high level training, are reasonably well regarded by the community and though there have been some cases of corruption the most likely contact most public ever have with police is probably because of a traffic offence though there is also a high presence with drug detecting dogs in public places and at events like music performances.
10. Our laws here are much like most developed countries, assault, rape, theft, murder, drugs, drunkeness in public, having concealed weapons etc. all illegal; there being some consideration/introduction? of age curfews in some cities/towns where there have been problems.
Driving license ages vary state to state and if you google Drivers License NSW you'll find relevant sites.
No death penalty.

11.AM/PM and weather already stated as far milder but likely warmer summers, good beach weather and seas no problem you need to be concerned with.

Australians have their own accents but it'll also vary because of where people have immigrated from, a big mixture of English, Europeans and Asians in Australia, your english in this post being quite reasonable.

Like any country, just google any topic you are interested in getting more detail and you'll get many links.