Is there a "New Immigrant" queue at Customs in the Dallas/Ft Worth Airport?

DFW airport is one of the better managed ones. However, due to increased restrictions the situation can change dramatically. What was a decent time on one day can be very different on another. Also, being on dependent visa, make sure they are not required to go thru' general queue.

If flight is on time, you may be okay. If not, it could be challenging. For going from terminal to terminal, they would need to take train ... thus there is sometime involved there as well. If they are flying on AA with in US, they have habit of changing terminals at last moments. This can cause additional confusion, if they are first time travelers especially. If possible move the domestic flight to give them close to 5 hours. They may end up waiting at the airport for a while. After such a long journey and going thru' customs etc., it should be a welcome change to catch their breath anyway.

That depends on how many people are in line.

There are different lines for U.S. passport holders and others.

It usually takes up to 1 hour to get through, so 2 hours 40 minutes should give you a margin in case there are lots of people there at the same time.

The airlines schedules flights so the people are spread out but sometimes the planes are not on time and too many people are there.

The whole process normally takes less then an hour and you will probably be at baggage claim before your luggage gets there. You should have plenty of time.