I'd like to find a Twilestia story where they're already in a relationship, kind of like Adventures in Home Ownership. (That one's my favorite)

5610975
Heh. Just thought of one and then realized you wrote it.

Well, there are my fics Progress and Forever and Again, both set after Twilight and Celestia have entered into a relationship.

Adventures in Home Ownership? Sounds interesting. Is it a story on here?

5611346 https://www.fimfiction.net/story/204927/adventures-in-homeownership-with-sunny-skies-and-dusky-sparks

5611357 You guys made it sound interesting, but the story looks dead. I'm also not a fan of reading stories with very short chapters.

5611638
Don't let that stop you. The story's excellent. It's episodic, so it doesn't lose anything by being incomplete.

5610975
I made it through D on my list, but it's not easy on a phone. Here are a few to get you started :

A Changeling Heart by SoniContinuum
A Night that Lasts Forever by Silver Scrolls
Celestia Doesn't Sweat The Small Stuff by gchamp89
Celestia's Desire by Hyzaku
Distance by Friendly Uncle

5612084 It doesn't look like it's going to be completed, though. It's been over a year since it last updated.

5612167
That’s what I was talking about. The chapters are mostly self contained, so there's no over-arching plot to miss out on, even if it never gets completed.

This was my review from my "fics I've read" file:

Adventures in Homeownership with Sunny Skies and Dusky Sparks by Honey Mead
Incomplete
Who confesses: already together
Twilight convinces Celestia to take a decade off in disguise so they can live as a normal couple.
Twilight angsts when things go wrong. Lots of adorable scenes, wonderfully done. Last update
September 2014

Say It by HermitKlam a series of short fluffy Twilestia stories.