Mark88

No, just sort it out at the appointment.

Your question is very broad, so you will get a limited amount of answers. There are many reports here on VJ if you look for them. You can find an example here:

For what do you want a lawyer? Either claim citizenship if your sister meets the physical presence requirements, or file I-130.

It should work out, but she needs to start NOW.

@SalishSea the OP writes, that "he and his sister were born int he US". That makes them USC by jus soli. Further the OP writes, that the family returned to Brazil, when the sister was just over a year old. If there weren't any larger breaks, the sister was now more than the required one year in the US. The children are under 18 and born before 11 June 2017. That is why the OP specificly mentioned the pre 2017 bdate, and the this means the "old" rule applies. The old rule (other than the new rule) does not require physcial presence above a certain age, just physical presence prior to the childs birth. The link I posted above will give you the official embassy information: https://it.usembassy.gov/u-s-citizen-services/child-family-matters/birth/crba-1/ "Old" rule: For children born on or before June 11, 2017: A child born outside of the United States and out of wedlock to a U.S. citizen mother may acquire U.S. citizenship if the mother was physically present in the United States or one of its outlying possessions for one continuous year (365 days) prior to the birth of the child. "New" rule: For children born on or after June 12, 2017: A child born outside of the United States out of wedlock to a U.S. citizen mother may acquire U.S. citizenship at birth if the mother was physically present in the United States, or one of its outlying possession, for a period of five years, two of which were after the age of fourteen, prior to the birth of the child.

Basicly yes. Rules like after she was 14 y/o don't apply. Proofing her one year physical presende will be a whole differnt matter. https://it.usembassy.gov/u-s-citizen-services/child-family-matters/birth/crba-1/

I second @iwannaplay54. It will depend alot on the officer, but expect it not to be easy and you needing to provide proof down to weeks spent in the US. You can see our case how hard it was:

Nope, just good old email, calling etc. Sometimes you even need to send a physical letter for enquiry. I had many times the spam filter blocking my emails to them.