"'And this is Nymphadora -'
'Don't call me Nymphadora, Remus'"
"'Nymphadora Tonks, who prefers to be known by her surname only,' finished Lupin."
"So would you if your fool of a mother had called you Nymphadora," muttered Tonks.
Page 57
"Lupin and Tonks followed, carrying Harry's trunk between them." (Lots of Remus/Tonks interaction like this. JKR likes to put those two together)
Page 112
"Lupin and Tonks sitting there."
Page 113
"Lupin glanced at Harry, then said to Tonks, 'What were you saying about Scrimgeour?'" (Noticing Harry's discomfort, but wanting to continue his conversation with Tonks)
Page 764
"Next to Tonks was Lupin."
Page 765
"Anyway, that's not the point," interjected Tonks. "The point is, if we find out you've been horrible to Harry -'
"- And make no mistake, we'll hear about it," added Lupin pleasantly. (Once more, the fun banter of finishing each other's sentences)