Can my father file for I-130 and AOS while on visitor visa?

I am afraid your attorney is mistaken. It is true that, when your grandmother will become a lawful permanent resident, she will be able to file an immigrant petition for her son. What's not true is that your dad could then come to the U.S. on a tourist visa and then adjust status. First, if he comes to the U.S. on a tourist visa while knowing that he is going to stay and become an immigrant, that constitutes a visa fraud. If USCIS finds that your father's application for a tourist visa was fraudulent, his application for green card will be denied, and he will be deported and barred from coming to the U.S. in any status. There are tricks to avoid the USCIS determination of a visa fraud, but It is highly unethical for your attorney to suggest doing it. And you can expect that the one who is willing to teach you how to deceive the U.S. Government will have no problem lying to you. Second, a permanent resident can sponsor her adult son only if he is not married, and he would have to wait for his immigrant visa for years. Every year, only a limited number of immigrant visas is issued; many more people petition for their relatives. The result is a backlog, a queue in which everyone has to wait for his/her turn. In the F2B category (unmarried adult sona and daughters of permanent residents), immigrant visas are now being given to the beneficiaries of the petitions that were filed in the fall of 2004 (for most countries; for Philippines - January 2002, for Mexico - August 1992). So, depending on where your father was born, he would have to wait for his immigrant visa no less than 8 years after his mother files a petition for him. If he becomes illegal in the U.S., the immigrant visa will not help him because he would become ineligible to receive a green card. While it might be possible for him to get en extension of his original B1/B2 status for up to 6 months, and it could be possible to change his status to a student visa, it appears very problematic that he can stay in the U.S. in a legal status all the years that he will have to wait for his immigrant visa. Please understand, I am not saying that it is impossible, but that it will take a lot of preparation, and might fail any time if USCIS denies any of the extensions or changes of status your father would have to ask for. One thing you need to understand: if your grandmother becomes an permanent resident and files for your father, he cannot come to the U.S. on a tourist visa and just stay until his number in the queue comes up - if he becomes illegal, he will not be able to get a green card even with an immigrant visa in his hand.

If your US citizen aunt files for your grandmother, her mother, that would be an immediate relative filing. She would be able to adjust her status without a wait for an available visa. If your grandmother, then a green card holder, were to then file for her son, he would gain a priority date but would not be eligible to adjust for many years. See the Department of State Visa Bulletin to get an idea of how long the wait will be. If you are a US citizen, and over 21, you could file an I-130 for your father however, and he would be an immediate relative.

No, this is not correct because your father would not qualify as an immediate relative since he is over the age of 21 and therefore, he would need to wait until a priority date would become available and that can take 4-6 years or longer in some cases. In order for him to be able to file AOS, he needs to be in status at the time of filing and he can only file when the visa becomes available. It is not possible for him to maintain lawful status as a visitor in the US for 4-6 years. If you are a US citizen and his child, then you can petition for him and that would be an immediate relative petition but it would have to be timed in the right way for him to be able to immigrate.

This is not advisable, he should apply for his permanent resident abroad at the US Consulate once his priority date is current after the I-130 has been approved. If he comes in on a tourist visa and tries to adjust status it is likely to be denied as he will be deemed to have lied when he entered. This is because a foreign national is not allowed to have immigration intent when coming into the US on a tourist visa.

An LPR can file I-130 for their unmarried son. There's a long quota, and no right to stay here while waiting for the quota.