Here we have the Sparkle family's huge and messy family tree.
Red = Romantic relationship
Blue = Adoption
Green = Siblings
Rings = Married
Heart = Love
Heart on fire = One night stand
Broken heart = Broke up
Broken rings = Divorced
Spike was officially adopted by Night Light and Velvet after Twilight hatched him at her entry exam. He was raised as one of the family but was always especially close with Twilight.
When Twilight married Flash Sentry Spike decided to move out and become more independent, so he started working as Luna's personal assistant. With time the two realised they really enjoyed spending time together and started actually dating instead, in secret. More on their whole relationship here:
Luna has some hang-ups on their age difference still that makes it difficult for her to be open to the public about their relationship even though she do really love Spike. For any bystander there is no doubt that they are a couple even though there hasn't been any official announcement. Spike lives in Canterlot castle but doesn't officially share a room with Luna even though they do spend the majority of their time in hers.
They have a daughter together named Noctis. The pregnancy came as a surprise for everyone since there had never been a dragon/pony hybrid before.
The oldest of the Sparkle siblings, Shining Armor, is married to Princess mi Amore Cadenza. They have three children together. Flurry Heart is the oldest and has a rare maneloss disease similar to alopecia. More on that here:
Their two younger kids are Nacre Shell and Riposte.
Twilight has had a rocky love life to say the least.
She met Flash Sentry while visiting her brother in the Crystal Empire. She recognised him from his human double in the mirrorverse and decided to strike up a conversation. The two found they liked eachothers company and Twilight asked him out on a date. After about 2 years Flash proposed and the couple got married after which they soon had a son, Inkwell.
Around the time that Inkwell was born there was a peak in disapearances in Ponyville and Canterlot. Flash was working as a guard so part of his job was to figure out what was going on, in combination with Twilight's royal duties and her running a school there was little time for either of them to spend with their son. This was a strain on their marriage as they both felt guilty yet resorted to blame one another for the neglect of their son, on top of everything Flash also felt like a failure when it came to the case of the missing ponies and the lack of progress and started drinking quite heavily. Some more info here:
Twilight couldn't cope with all that was going on and decided that they needed to get a divorce. Flash held a grudge throughout the entire process and hasn't been in touch with his old family since they separated.
The divorce was really hard on Twilight who in all her sadness found some comfort in Sunburst. The two had become quite close friends and Twilight would invite him over often to talk about her old relationship and everything that had went wrong, Sunburst in turn would vent about his lacklustre love life. The two sort of just happened to become a couple. Sunburst moved in with Twilight and the two later had a daughter, Marigold, together. As time progressed they both realised that neither of them really loved eachother, they were still really good friends but nothing more. It again saddened Twilight to split up with yet another partner but this time it was on better terms and they both stayed in touch with eachother. Sunburst got joint custody of Marigold and she would stay with him every other week.
Quite some time later Sunburst and Thorax got married and had a surprise clutch of 7 changeling grubs. More on that in a future sketchdump.
Twilight once again on her own felt sad and lonely. During a event in Canterlot castle she had a few to many and started hitting on the yak chief Rutherford. The two had a one night stand that to Twilight's horror ended up with her getting pregnant. She was hesitant to keep the child or even if she should tell Rutherford at first but she eventually came clean to him. He was extatic to become a father which made her more at ease with keeping the child.
After her third child Love Letter was born she slowly started dating Starlight whom had been there for her throughout her pregnancy. Starlight practically became a second mother for Love Letter and the two are very close. Starlight and Twilight have no plans on getting married or having any children together, instead they live life one day at a trying their best to keep their family together.
Lots of text, probably with a lot of spelling and grammar errors but to be frank I have no energy to fix them haha.
I could have made the whole tree bigger by including Celestia's kid and partners as well as Pharynx family but decided to contain everything to whose closest to the Sparkle siblings