Falls asleep on the couch: Saionji. He's often in the dog-house.
Makes friends with the neighbors: Nanami, though she prefers the term "underlings."
Is the adventurous eater: Saionji's the cook, so naturally it's him.
Hogs the covers at night: Nanami is THE Blanket-Hogger Professional.
Forgets to do the dishes: Nanami would insist on Saionji doing all the chores at first, but after some Character Development, starts helping out in the kitchen herself.
Tries to surprise their partner more often: Surprises tend to lead to misunderstanding shenanigans, so they tend to prefer to ask each other first.
Leaves dirty laundry on the floor: Both before they decide "fuck it" and pick up after themselves.
Stays up til 2 AM reading: Maybe Nanami, but unlikely. Saionji prefers fencing.
Sings in the shower: Nanami sings some notes to herself if she's in a particularly good mood.
Takes the selfies: Nanami, definitely.
Plans date night: Nanami, and she'd be quite proud having her arm around Saionji's and leading him around/showing him off at parties.
Drinks all the coffee: Saionji prefers a small cup, he's neutral toward it.
Brings up adopting a pet: None. Nanami doesn't want a repeat of what happened with Touga's old cat. :( They've already got Touga's new cat to look after anyway.
Always ends up with too much junk food after grocery shopping: Nanami. Let's hope Anthy doesn't curse her again.
Nicknames the other: None, they're good with each other's names. Saionji may refer to her as "mistress" though. :o