US Immigration from Sri Lanka

We have gone through I-130 process and just got the visa for wife and two kids.

(below 18 years old) they have I-551 stamp on their foreign passports.
Question is how do I apply certificate of citizenship for my two kids ?
What process involved ?

As a sponsor how much income we need show according to poverty guidelines (as a percentage )?

I would like to enroll my two children to a high rated elementary school in my school district.

Can we select the school we want to enroll them in ? The closest one is not rated good.

Hello, my father entered USA with the immigration visa (IR5) a few days ago. He has the passport sealed by the immigration folks at the airport, no issues. My poor mom still didn't get her visa (due to the issues mentioned here):

So she is all alone back in Sri Lanka. My dad entered the US only because he had to before Nov 30th according to the visa restriction.

My father wants to travel back to SL to help my mother get her visa as soon as possible. They are sure she is at the last leg of her visa process (lots of effort going on to get her issues resolved).

My question is, can he travel now? He doesn't have a physical green card. All he has is the seal on the passport. He has only been here in the US for about a week.

Hello, I'm sponsoring my parents for their green cards. They went to the interview at the US embassy in our home country (Sri Lanka) yesterday. Dad got approved but mom's has a request for a document. This is for a police report. She worked in Bahrain about 42 years ago for about 12 months. She doesn't have any documents related to that stay any more. No old passports, or any ID she might have had in Bahrain. It all got destroyed in a fire. When I tried to obtain a police report from Bahrain they informed me that they will not be able to do so without an ID she might have used there all those years ago. The person I chat with wasn't even sure if they had the same ID system all those years ago. So I mentioned this when submitting docs to NVC and we got DQ'd. We were able to get police report for other places she lived. At the embassy though they have sent her back with a request for a police report. She had tried to explain but they shut her down with 'Nope we need a report'. We don't even have a Bahrain embassy in Sri Lanka. What do we do in this situation? I'm sure people have gone through the same situation.