Entry and Exit question

You will get an exit stamp and brief security interview in Amsterdam (the interview's not common at other European airports). Nothing related to customs.

Then you and all your luggage will go through US immigration and customs/agricultural inspection at your first port of entry to the US, even if you have another connecting flight.

On the way in, you will get your passport stamped (immigration) at Lisbon for entering the Schengen Area.
You say "required to get passport stamped", you don't have to worry about getting it stamped, they won't let you through into luggage reclaim until you have passed through passport control.
On the way back, it will get stamped at Amsterdam for exiting the Schengen Area.

Everything else is intra-Schengen and no official passport checks, though the airlines will want to see your passport as an ID check.

Customs into the EU will be where you retrieve your bags (is Lisbon to Seville a connecting flight or a different day?), but customs is random checks only. There is no customs on exiting the EU.

Lisbon to Seville will be a few days later. We will have small carry on luggage only for trip, as the size restrictions for carry on for the regional flight between Lisbon and Seville is smaller than standards for US domestic flights. We didn't want to have to worry about bag check/ claims when connecting and doing several locations between Portugal and Spain.

If the teens are minors ( less than 18) be sure to have the necessary documentation from the absent parent to travel internationally.

Yes, thank you. I confirmed with the airline and Embassies to make sure I have necessary documentation.

I recently connected through Schiphol from Budapest going to San Francisco and the agent merely glanced at my passport and me and stamped it; I noticed others being asked questions re their stay and reason for visiting. This added perhaps 10 minutes to my journey through the airport, and they do have a special line for short connections with an agent deciding if your connection is short, not you.

There also may be passport controls when you don't expect them, as well as showing your passport after passport control. We just flew to France (Lyon) from the US via Amsterdam, and besides going through passport control in Amsterdam each way (as expected), we had to go through passport control in Lyon both ways. I assume that's because France still has a declared state of emergency. We also had to show our passports multiple times besides at passport control.

Thank you.I am hopeful that two hours between landing in Amsterdam and take iff for Atlanta will be enough time to pass through all passport checks.

My experience was the same as Robert's inbound to Nice via Amsterdam.

I thought Amsterdam seemed a well-managed airport

How does that work? Do you wait in a line and when you get to the agent, if he or she thinks the connection is long enough, are you then told to go to the back of the regular passport control lines?

When I was transferring recently, I saw a sign for a short connection line, but it was blocked off. Some people did approach an agent there, apparently to ask about that, but I didn't see the line ever get opened. I wasn't paying too much attention because we had plenty of time.

I am hopeful that two hours between landing in Amsterdam and take iff for Atlanta will be enough time to pass through all passport checks.

That will be plenty of time as long as your first flight isn't significantly delayed. We connected in Amsterdam coming (mid-April) and going (last Sunday), and it was very quick. It was helped by the fact that we never left the secure area (even though on the way back we were bused from the plane to the terminal), so we didn't have to go through security there.