Crediting User kimbrlyc for being the only person I've seen on this page to bring this up, but there is definitely a reason why the Crain children represent the five senses; as well as there being evidence for each one of them having their own specific sense.

Here's the breakdown:

Stephen - Sight

Shirley - Taste (or perhaps Speech)

Theo - Touch

Luke - Smell

Nellie - Hearing

Theory: Each of the Crain children have these as their special sense because they are meant to represent a body; and in turn, all of them *together are meant to represent a home.

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• Stephen's sense is specifically sight because he is the only one that sees Hugh's dead body when they finally leave Hill House, and is typically the only one who sees the house's ghosts in the daylight as a child (i.e. the old clock worker in overalls). Also, notice that he is the only one that sees Young Luke in the tree house - no other character truly sees the existence of the different, friendly iterations of the Red Room save for Steve. This ties into his whole character needing concrete evidence of everything. As Leigh says, he needs to process it all as reality and rationalize things in order to really believe it. What is the best evidence of anything? Seeing it for yourself. Also, his episode is literally called, "Stephen Sees A Ghost". Yes, each of the other children see specific ghosts as they are each haunted throughout the series, but Stephen is the only one that sees ghosts that everyone else doesn't see. (The Bent-Neck Lady is Nell's personal ghost, but then again, it is really just her haunting herself and not really a ghost of the house until later.)

• Shirley is a very interesting case because taste is not necessarily the forefront as a sense associated with her; but her Crain Quirk (as it were) is involved with her mouth. She talks in her sleep; she mentions "dancing in the Red Room" over and over again in the beginning of Episode 1, and says "Nellie's in the Red Room" when all the siblings wake up at the feeling of Nell dying at Hill House. She is a kind of conduit for the house; the mouth, the communicator. It is also no surprise that she shares the name of the original author of the novel from which this series is pulled from: Shirley Jackson. Jackson was the orator for the original story just as Shirley is for the happenings in Hill House. Again, hers is a bit of a stretch, but each of these instances are present as evidence.

• Theo is pretty straight forward. She feels ghosts - in Hill House, she can sense where ghosts are and where the previous residents have been. Her entire episode focuses on this talent both in Hill House and outside of it; and it's pretty obvious because her episode is called, "Touch". Enough said.

• Luke's sense of smell is sneaky, but nonetheless there. Remember when he and Nell found the telephone system in the house in Episode 3? He tells Young Theo in the bedroom upstairs, "Ewh, what's that smell?" Theo brushes this off, but Luke again asks, "You really don't smell that?" Later on in Episode 7, when an older Theo walks in after trying to sober up with a shower, Luke looks at her. He mentions a hangover cure that will mask how Theo smells.

• Finally, Nellie and her sense being that of hearing. In Episode 3, Olivia tells Young Theo that it is peculiar that when asked about what she thought about the house, Nellie said that it was "loud". Also note that in Episodes 1 and 5, we see that Nellie is dancing throughout Hill House by herself. She is hearing music inside her own head that is being produced by the house's influence on her in the moments before she ultimately dies.

• *Side Note - Hugh and Olivia are technically excluded from this theory because they are not obviously shown to have particular "gifts" or specific special senses in comparison to the children; but they could be seen as other essential parts of the family's body. For instance, Hugh can be seen as the limbs because he is the actual craftsman for the house flipping. He also says that he "didn't have enough arms for the children" when their family fell apart. Olivia can be sort of the brain: she plans the layout of the houses that she and Hugh flip. Additionally, her mental state is the one that is really destroyed in comparison to the rest of the Crain family while she is alive. In a more romantic sense, Hugh is of the physical world while Olivia is more metaphysical in a sense. Without each other, there is no equilibrium for the body.

So, why did the creators of this series choose to include each of these Crain Quirks throughout the show? If we know anything about this series, we know that nothing is done on accident. It's a cool addition to the characters, but it's really so much more than that. I didn't realize it until I re-listened to Nellie's final monologue in the last episode.
Nell tells her siblings while they are trapped in the Red Room that their mother says "a house is like a body". Nellie then goes on to explain that the Red Room is like "the heart of the house; no not a heart...a stomach." Then, what's the heart of the house? Metaphorically, the family that lives inside it.
The Crain Family together compromise a complete body, full of senses that are essential to survival. Without each other, the Crains fall apart and the body ceases to function properly. That's why when Luke says, "I don't know how to do this without you", it is all the more heart-breaking because it is like their family will forever be crippled without Nellie. But when Nellie reassures him that she is not gone (and is instead sprinkled all over her siblings' life), she allows the remaining Crain siblings to trust that they can continue to live on; not only as one body, but as a complete home.

Any questions, comments, concerns? Naysayers? Let's talk about it!