newacct

A derivative beneficiary can enter at the same time as, or any time after, the principal beneficiary enters.

Yes, because, assuming they left before their AOS was approved, their GCs were issued in error. Leaving the US while their Adjustment of Status (I-485) was pending automatically abandons their AOS, unless they had H1b/H4/L1/L2/K3/K4/V status before they left (which they didn't) or they were granted Advance Parole before they left (they weren't). It's quite possible that the immigration officers won't notice this, and they will be able to enter, but at any future time when they apply for any benefit, e.g. naturalization, or in a future entry, it can be noticed and they can be denied entry. If they are let into the US somehow, it should be possible for them to do AOS again.

You cannot petition a niece. So I am guessing you petitioned your brother or sister, and the niece is an unmarried under-21 (according to CSPA) child of the principal beneficiary, so she is immigrating as a derivative beneficiary. If so, she cannot get married before entering the US with her immigrant visa, or she will not qualify as a derivative beneficiary anymore. She cannot get an "actual green card" before going to the US, because only permanent residents can have green cards, and she does not become a permanent resident until she enters the US with her immigrant visa.

Yes. The date you file the I-130 becomes the priority date of the petition, and each month's VB determines whether a petition with that priority date and category can do Adjustment of Status/Consular Processing.

See 9 FAM 302.1-9(B)(1)(c)(4)(b):

I'm not sure what your question is. You can always file I-130 for your spouse after your marriage. The visa bulletin matters for timing of the Consular Processing or Adjustment of Status process.

You compare the date she left and the decision date on the notice.

Not if she leaves before the decision is made, which is likely since she only intends to stay for 25 days and I-539 can take 6 months.

1. yes 2. for as long as it is pending, with no limit 3. no, as long as she leaves while it is pending, or it is approved

Dual citizenship cannot be "against" any country's law -- it is simply a condition that arises when one country's law says a person is a citizen and another country's law also says the person is a citizen. If a country doesn't want dual citizenship to occur, it is free to make its laws for obtaining citizenship and/or taking away citizenship such that it dual citizenship doesn't occur in those cases. People sometimes oversimplify dual citizenship restrictions and say a country "does not allow dual citizenship", but no country's law actually says that -- rather, you need to look at the country's specific laws to see how it treats each case in which dual citizenship can happen. Some countries have a restriction in one case but not the other. And, as far as I know, in every country on Earth, there are certain situations in which the country's law will grant citizenship to a child at birth even if the child has another citizenship at birth. Nothing in India's constitution or laws says dual citizenship is "not allowed". Rather, there is a provision in the constitution and Citizenship Act that says an Indian citizen who voluntarily acquires a foreign citizenship automatically loses Indian citizenship. There is a provision in the Citizenship Act that says undertaking to renounce existing citizenship is a qualification of naturalization. But neither of these rules deal with citizenship at birth. Neither the provisions for Indian citizenship "by birth" (birth in India) nor Indian citizenship "by descent" (birth outside India) are conditioned on the child not having another country's citizenship at birth.

Yes, if your brother's daughter has not aged out, and still qualifies as his derivative beneficiary, she can immigrate to the US with him, and then he can surrender his green card after she enters (thus becoming a permanent resident), and it would not affect her permanent resident status.

1. The new public charge inadmissibility rule is not currently in effect as it has been blocked by a nationwide injunction 2. Neither Obamacare nor any subsidies or tax credits are considered under the new public charge inadmissibility rule 3. Inadmissibility is not relevant in naturalization, and green card holders are not affected by inadmissibility rules, unless they leave the US for more than 180 days at a time or engage in illegal activity while abroad

India doesn't "pretend" the child doesn't have US citizenship. Indian law says that a child born abroad to an Indian citizen parent is an Indian citizen by descent if registered at an Indian consulate within one year of birth with the parents declaring that the child does not hold a foreign passport. It does not depend on whether the child has another citizenship. The same law says that an Indian citizen by descent will cease to be an Indian citizen if they do not renounce their other citizenships with 6 months of full age, so it clearly contemplates that they can have other citizenships before then.

You are wrong. A child born in the US (not to a diplomat with full diplomatic immunity), or born outside the US to a US citizen parent who meets the conditions to transmit citizenship to a child born abroad, is automatically and involuntarily a US citizen at birth. The US law says "The following shall be nationals and citizens of the United States at birth". No action needs to be taken for this to happen, and neither the parent nor child has any "choice" in the matter. The child can renounce citizenship when they are old enough to have the maturity and understanding to voluntarily renounce (usually at least 16).

The child is either a US citizen at birth or not. There is no "claim". If one parent had full diplomatic immunity at the time the child was born, and the other parent was not a US citizen, the child is not a US citizen at birth, and there is no way to choose or "claim" US citizenship for the child. The parents have the option to register the child as a US permanent resident (green card holder) if the child has lived in the US continuously since birth. Note that generally only high-level diplomats have full diplomatic immunity; non-diplomatic staff often have a limited form of immunity for official acts; this does not count as full diplomatic immunity and their children born in the US are automatically US citizens. Here is an old edition of a section of the Foreign Affairs Manual that talks about citizenship at birth for children of diplomats. Scroll down to 7 FAM 1116.2–3 (on page 9–10 of the PDF) for the section on representatives to the UN. (Unfortunately, the current version of the Foreign Affairs Manual does not contain comparable information.) If one parent had full diplomatic immunity but the other parent was a US citizen at the time of the child's birth, whether the child has US citizenship is determined based whether the US citizen parent meets the conditions to transmit US citizenship to a child born abroad. If neither parent had full diplomatic immunity at the time the child was born, the child is automatically and involuntarily a US citizen at birth.