I guess I will choose three, like RJ did. Jackbear (Jacklynn x Nightmare Fredbear), Blazing (Blaze x Lightning), and Shadow Oceans (Kasey x Krystal).

Krystal belongs to:

Which hogs the blanket?
Jacklynn would try to. But then it may just end up in a cuddling session between the two because she accidentally woke Fred up.
Lightning, because Blaze does not sleep with a blanket, so more warmth for the shy bean.
If they have to share, Krystal, because Kasey would offer to sleep on the floor. And besides, when Kasey is hot, she sleeps with minimal coverings.

Which one cuts the other's hair?
Fred, because Kya would urge him as she can't approach Jacklynn with scissors or any fashion device.
They dont have hair.
Kasey, because her mamá taught her thid, and also, her hair is a nightmare to deal with.

Which one makes coffee (or tea) for the other in the morning?
Fred most likely will make hot chocolate for the both of them. Especially if it is cold.
Lightning makes this herbal tea that relaxes both him and Blaze.
Kasey would make the tea because she would already be up at 5 in the morning for no reason in particular.

Which one picks up the pizza?
They would make the pizza! If not, then Fredbear would pick it up.
Imagine them having pizza for the first time...anyway, Blaze would Definetly pick it up.
Kasey, because she would try to sneak a piece of garlic bread for the shadows without Krystal noticing. Key word "try".

Which one likes their music on full volume?
Jacklynn, and she will get up and dance to it ridiculously.
Surprisingly enough, Lightning, as he likes calm meditation music over the sound of anything else.
Kasey, as anyone can and will tell you about me playing music while doing dishes.

Which one complains about the crumbs in the bed?
I honestly dont think they would be complaining, and if they do, they'd be too lazy to deal with it anyway.
Both complain, and both will fix it.
Krystal, when she realizes that SOMEONE had to have had fed the shadows some left over cookies.

Which one is ticklish?
Jacklynn.
Lightning.
Kasey. (I am giggling about it even as I write this)

Which one sings and which one plays the music?
Jacklynn plays the guitar while Fred sings cheesy songs, and when they are both laughing, Jackie will join in.
Blaze has a surprisingly good singing voice, but would rather have Lightning sing while he plays the drums or a flute.
Both sing, and hopefully Kasey will not forget the lyrics in the middle of the song.

Which one proposes? (Ooooh me feels)
Fredbear would, probably very shyly, but then it completely turn around when Jack tackles him in a hug and says "Yes!" Over and over.
Actually, Blaze proposed mid-battle with Lightning, and Skullkid hurriedly married them before smashing two enemies to the ground. Almost a year after the war, Blaze brought that up with Lightning, did an actual, romantic proposal, and got married a few days later.
Extremely spurr of the moment, but top that crazy proposal!
Krystal would attempt to. It would probably be after a long day of hanging out together, and they are resting near the shadows, when Chaos is telling Krystal to "do the thing!" And Kasey would have no idea, until Krystal dropped down on one knee. When she accepts (because I certainly would), they would hug, and proceed to be piled on by shadows, happy that their Alphas found a mate.
And Mr.Batey would eat the rest of the cookies while they do so.

If you guys wanna do this, suit yourself!