No, not in the USA. You have to go through the Immigration process, and they will probably make you go to your home country first. Consult a good immigration lawyer, for any exceptions.
no depends were they came from
if you overstayed your visa you will be banned from Australia for three years
If you overstayed less than 6 month you will be banned to entering the US for 3 Years, and if you overstayed more than 6 Month you will be banned for 10 Years (AG)
You are right in thinking that you need to start resolving the issue now. Check in with a reputable immigration lawyer.
No, you have to marry to get a visa.
file a petition for him
well many things happen and it is in a secrect file that no one can know
There is no way for that person to becme a citizen immediately. Once the children reach the age of 21, they can sponsor the person for residency, but it is a long process.
Yes. Because you came into the u.s. legally.When you get married your spouse should file petition I-130,green card application and work permit. Please talk to a immigration lawyer for help. On another note. You have to file several forms. I-485 Adjust Status- Because he came legally but overstayed I-130 Petition for Relative - Filed by you to claim your husband I-864 Affidavit of support- You have to prove you can support your spouse 125% while his working papers are pending.
You can, but, you may get deported if your not legal to be in the States.
nothing she tills has to become a citizen
The same way you marry a girlfriend that has not overstayed. Getting married has nothing to do with immigration law. However, any falsification on the marriage license can invalidate the marriage. Being in the country illegally will not change based on marital status. If you really want to get married and have a long relationship, consult an immigration attorney.