US citizen sponsoring to-be spouse and stepdaughter living in India

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Please advise on the questions.
I am a US citizen. My to-be wife and to-be stepdaughter are in India, and Indian citizens. My to-be wife has a valid US visa (business visa) for 5 more years. I would like to explore the options on how to obtain the Green Card and EAD for her and the daughter.

Following are the options that I am considering.

Option 1. Marry her in India and she applies for Green Card from India for her and the daughter. From what I understand, it may take 3 months, 6 months, or even a year for it to be processed either from Delhi, or Mumbai.

My question:
While she is waiting for the (temporary) Green card, can she travel to the US under visitor visa, or business visa? The issue is, for her job, she has to travel to the US frequently. As because the immigration visa (temporary Green Card application) is pending, does that prevent her from travelling to the US either under business visa, or visitor visa?

Option 2: Bring her to the US under fiancee visa and get married. But from what I understand, the processing time (wait time) in Delhi/Mumbai is about the same, as that of getting the (temporary) Green card. If so, fiancee visa does not do any good.

Option 3. She comes to the US using a legal valid visa (visitor, or uses her existing business visa). We get married in the US.

Question:
If we marry in the US, does she have to first obtain EAD, and temporary Green Card later?
How long does it take to obtain EAD and/or (temporary) Green Card.

Is there any age restriction for the daughter (over or under 18 year) for which I can sponsor the step-daughter?

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My question:
While she is waiting for the (temporary) Green card, can she travel to the US under visitor visa, or business visa? The issue is, for her job, she has to travel to the US frequently. As because the immigration visa (temporary Green Card application) is pending, does that prevent her from travelling to the US either under business visa, or visitor visa?

She can try. There is no rule that prohibits her from visiting, but it will be more likely that she will be denied entry

Option 3. She comes to the US using a legal valid visa (visitor, or uses her existing business visa). We get married in the US.

It's okay to enter on a visitor visa intending to marry and then leave. She is not supposed to enter on a visitor visa intending to file Adjustment of Status during that stay.

Question:
If we marry in the US, does she have to first obtain EAD, and temporary Green Card later?
How long does it take to obtain EAD and/or (temporary) Green Card.

She can apply for Adjustment of Status. This can take almost a year, sometimes more. She can optionally apply for EAD and for Advance Parole, both for free, when she applies for Adjustment of Status, to work and/or leave the US while her AOS is pending. She doesn't have to, but since it's free, there's no downside. The EAD/AP might take about 5 months to get.

Is there any age restriction for the daughter (over or under 18 year) for which I can sponsor the step-daughter?

As long as you marry before she turns 18, you can petition her.