Against the order you typed, which came to $1,536 a person.
Your flights, one line per ticket. Each button opens the fare on the site that sells it, so nothing is booked here. Tick a line once you've paid.
Total $1,219 per person · $2,438 for 2
Times, bags and other sitesStart with Dallas to London: it’s the biggest fare, so it’s the one you least want to lose.
With a free account you can change a trip by typing, like “four nights in London”, and it re-plans in seconds.
Your Dallas → London flight can connect through Madrid with a gap of 25h. That's about 13 daylight hours in the city, once you are through the airport at both ends. It runs overnight, so you need somewhere to sleep, or to stay up. It costs $43 more than the cheapest fare for that leg (and $98 less than booking Dallas → Madrid and Madrid → London separately).
Your London → Athens flight can connect through Istanbul with a gap of 22h. That's about 15 daylight hours in the city, once you are through the airport at both ends. It runs overnight, so you need somewhere to sleep, or to stay up. It costs $13 more than the cheapest fare for that leg.