The only reason I didn’t make this family tree earlier is because I had no idea how to format a poly throupleeeee
 
Starlight Glimmer and Sunburst’s family and friends always knew they would end up together. So when the two made their relationship public and later got married, no one was too surprised by it. They were happy in their marriage, Starlight moving to the Crystal Empire as a part of Candence’s court and to live with her husband. But soon, Starlight and Sunburst wanted to add to their lives, confiding in Twilight that they didn’t know where to begin. Fortunately, Twilight seemed to know exactly who to introduce them to. They met Moondancer on a visit to Canterlot, Twilight spending time with the three of them as their mutual friend. It didn’t seem to long for Moondancer, Sunburst, and Starlight to bond and grow as friends. After some time, Starlight and Sunburst invited Moony to join them in their relationship, and she was more than happy to accept. The three are all romantic together, but with Starlight and Moondancer seeming more so than Sunburst and Moony. And they are all completely satisfied with their poly relationship, still giving Moondancer the space and freedom she wants without tying the knot and settling outside of Canterlot, and allowing Starlight Glimmer and Sunburst to dote on Moony while they all nerd out together.
 
After years of being together, the three decided that they were interesting in having a child together. And with Sunburst’s ridiculous amount of knowledge and Starlight and Moondancer’s immense magical power, it wasn’t too difficult to tweak an old spell to conceive a child that was the biological offspring of all three of them. Being made from intense magic, it wasn’t much of a surprise when their foal showed innate magical ability. Starfire grew up being coddled by all three of his parents, with each parent showing their affection in different ways. Moondancer was always ready to read to Star, the two usually sitting next to a fire with a stack of books. Starlight Glimmer gave love by practicing magic and teaching him new spells, always pulling him into a big bear hug whenever a new lesson turned out successful. And Sunburst, with his knowledge of foals thanks to being the royal family’s Crystaller, spoiled his little colt with things he knew made other foals happy: ice cream, candy, toys, and tickle fights.