Just a few questions for you... When you had them each in their own 20G tanks, what were their temperatures and humidity? What were you using as a substrate and heat source, and what did you have set up for hides?
In the larger enclosure, same questions.
What you are perceiving as 'happiness' for your snakes is not typical snake behaviour, but signs of stress and dominance. Ball Pythons typically spend all of their time hiding, they are nocturnal, and in the wild spend the majority of their time within rat burrows and termite mounds. In captivity they are not typically active animals, and the consistent use of their hides and thermo-regulation are signs of good husbandry.
Curling up together is either 1. breeding, or 2. competition for the best place in the enclosure, not that they enjoy one another's company. They are not mammals, and they do not behave like mammals when healthy and 'happy'. This is the reason why everyone has advised they should be separated, they are showing signs of competition and dominance and stress.
If while in their separate enclosures they were not eating for you, the husbandry itself being off is the most likely cause, not that they 'missed' one another or felt lack of companionship.