I just want to start by saying that I a great fan of your work. In aSoS Davos said that he expected Devan to be eventually made a knight. If Devan keeps to R'hllor is that possible?
Could be a problem there, but it's possible that Stannis will change the rituals.
Can someone who keeps to the old gods be made a knight too or is it a exclusive of the Seven?
The latter. Those who follow the old gods can be the northern equivilent of knights, but it's not quite the same.