1 and 2: You saw that right. Dark Roast and Dusk Constellation were technically coltfriends.

Since Dusk Constellation went to the RSF, he was up in Canterlot for a good chunk of his teens. During his study sessions (which he did often, considering he's the son of Twilight Sparkle, she taught him all she knows), he would head out to Donut Joe's cafe. They didn't click right away, with Dusk mostly getting annoyed and Dark Roast flirting up a storm, but eventually they fell into a situation where they preferred to be with each other to being alone.

It only came to an end when Dusk had to move back out to Ponyville and the farm, and with his newfound fame for being a stellar detective amping up, they just couldn't uphold the "friendship" they had before and fell out of contact. However… they might meet again, considering Dark Roast's place is right across from the Violet Dove, where Dusk happens to stay…

3. In the little simple style I'm testing out, I decided to draw a scene I had in my head for a while. I haven't really touched on it, but Starkrimson Nebula and Hazy Daydream were around each other a lot for a good portion of their youth. Mainly because Rainbow taught her children how to fly over Sweet Apple Acres, where Starkrimson lives. It came to a point where Dreamy seemed to crash near him on purpose (she came out remarkably unhurt after "crashing", hmmmm), or watch him just work in the fields, even after she was clearly able to fly. He didn't really get annoyed by it, but he just wasn't sure how to deal with the attention and told her off sometimes. Only sometimes. Other days he let her stay on her little cloud and watch while pretending not to notice her. She started visiting less and less, which he was secretly disappointed about, but it wasn't like he could just ask her why! It wasn't like they were a thing in the first place, and now he misses her?! Preposterous.

Starkrimson: Get off my property! W-well it's my dad's, but you have…. you have no right to hang around!
Daydream: Technically I'm not on your dad's property, I'm above it~

4. Like most of my characters, Old Fashioned Lavender lives in Canterlot. Prarie Plume, on the contrary, lives in Apploosa. So how do they meet, much less have a relationship? Well, Prarie's mother is Coco Pommel, so naturally she has family, other friends, and business in Canterlot. So it wasn't uncommon to Prarie to accompany her mother on her trips. There was no specific place, nor a specific time when Coco happened to introduce Prarie to her friend Fancy Pants, and his son Lavender. It simply happened, and soon enough, they were well aquainted. However, once Lavender got his job at the Violet Dove and Prarie started to build her company, they just drifted apart slowly. When they do see each other, which is rare, they are quite friendly with each other. The feelings they once had have dissipated, though they do like to chuckle about Lav's awkwardness.

Dark Roast is the son of Donut Joe and Fine Print
Dusk Constellation and Starkrimson Nebula are the sons of Twilight Sparkle and Big Mac (i tried to avoid doing two of their kids but its so hard LOL)
Hazy Daydream is the daughter of Rainbow Dash and Double Diamond
Old Fashioned Lavender is the son of Fancy Pants
Prarie Plume is the daughter of Coco Pommel and Braeburn