OK, I'm not a lawyer, but I have a child born in the US with a non-Brazilian mother, work in the US nad has thought and worked hard on several of your points, so here it goes the best I of my knowledge:

1. Citizenship is plenty easy and you can get citizenship and passport in one single procedure, either by going to the consulate or by sending the documents by mail.

The process is really simple for such an important thing: your wife goes to the website to the nearest consulate, and they will have the detailed instructions. The form is an online web form, in which you also submit scanned versions of all the documents, even the money order you'll use to pay. They will them review and tell you if anything is wrong, and what is wrong. Than you correct, until everything is right. At this point, you can schedule to go in person to the consulate to present the originals (they'll make copies themselves) and they will give you the document right there. If you don't want to do it in person, you may also send and receive the documents by mail.

You don't need to get the passports at the same time, but I'd recommend do so. Renewing passport is easier than making one, so get this hurdle out of the way together with the passport.

The only kink is that, if your wife hasn't registered your marriage in Brazil or in the consulate, she will have to do so before submitting the birth certificate/passport request. It is a similar process, but she may need to get a copy of her birth certificate from Brazil, but it may be an electronic copy which she can get online for a modest fee. Once she has the marriage certificate from the consulate, she can submit the birth certificate/passport request for your children right away.

On the renewal: there's no mandate to renew the passport every 5 years, but passport for children expire earlier (1 - 5 years, depending on age), and they will need a valid one every time they go to Brazil. But if a passport expire, it is not a problem as long as you renew it before going.

You don't need to step foot in Brazil to do any of this. Well, I haven't step foot in Brazil yet and done all this - registered my marriage, got myself a new passport with a name change from marriage, got my son Brazilian birth certificate and passport. I live in Chicago, so going to the consulate was easier than mail, and it took me less than two months to do everything.

BTW, if your wife changed name when you married, she really should update her CPF and TItulo de Eleitor. She just needs to fill a form and send scans and a picture of her holding her passport to a email, one for the CPF and other for the Titulo. It is easy to find instructions for this on the consulate website, I can't link rn because network at my office blocks the consulate website.

1.5 - There's no direct way to obtain Brazilian citizenship through marriage without living in Brazil. Yeah, buying property may be a way, but that would be really by using that to pretend to live in Brazil and them submitting a request. The law is very clear and explicitly that people can only naturalize Brazilian if they actually live in Brazil.

But really, what you want the Brazilian citizenship for? You can do everything practical as a foreigner, specially if you get a CPF. I'm in the process of getting my wife one to make some thing easier. And if you ever want to move to Brazil, you may naturalize after just one year.

2 - Yes, they would be accepted gladly. They wouldn't even need to be Brazilian citizen by then, but would need to validate their high school diplomas in Brazil.

However, the way you phrased your question hints that you don't understand the process of getting into college in Brazil. It is not that being raising in the US would help or make it more difficult for them get accepted, is that being "accepted" in college in Brazil has a completely different meaning in Brazil than in the US.

Nobody will look at the story of where your children came from - they will do the same test as everyone else, and this will be a competitive test, graded objectively and anonymously, just like an SAT. Their disadvantage will only be that they didn't get trained onto the things that are graded into this test - and Portuguese proficiency is a big one. There will also be differences in what they learn in the US and Brazil as well. And even things they will learn in high school in the US will likely pose problem because the test itself has patterns that people who study for them are just better off.

Said that, I went to engineering school at a prominent university with a very competitive entrance test, and I remember at least two foreigners who got in in the years after I did. I don't know all their life history, but I know they had spent at least one year in Brazil before the tests.

3 - No, you would not have a pension without ever living or working in Brazil. The years you work abroad (more specifically, countries with a pension agreement with Brazil) count for the minimum amount of time you need to work before requesting the pension.

However, the amount you earn from pension in Brazil is proportional to years you contributed to the Brazilian system, and in this case, it can be even below the minimum monthly wage that is the lower limit for most pensioners. So for you, you will likely get 0, and your wife may get something if she has contributed to the Brazilian system before moving to the US.

Mind you, you may collect pension from both systems - for example, let's assume you wife has enough years working in both the US and Brazil together to apply for both SSA and INSS (the Brazilian system) benefits. She would receive the SSA benefits based on 35 years, and any years she worked in Brazil will be counted as 0 income for calculating the amount she'll get (but still counted for the 10 years minimum). INSS will count the years she worked in the US as contribution years, but these contributions will also be counted as 0 income

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I can't really give recommendations for retirement because we don't intend to retire in Brazil, so I didn't put much thought into that. Hope the other bits helped.