Britney Spears was a no-show at her niece’s high school graduation — but her mom, dad, sister, and son gathered for a rare family reunion at the event. In pictures obtained by the Daily Mail , the famous family members donned their Sunday best to celebrate 17-year-old Maddie Aldridge’s big day. Britney’s father, who had his right leg amputated in 2023 following an infection, attended the event in a gray suit, while her mother Lynne Spears, 71, was seen in a cream dress with a matching blazer. Jamie Lynn, 35 — who at one point was snapped crying for joy while watching her daughter navigate the ceremony — wore a black mini dress with white puff sleeves. Britney’s eldest son Sean Preston , 20 — whom she shares with ex-husband Kevin Federline, along with son Jayden James, 19 — donned a casual white polo shirt for the outing. He was seen proudly holding up a photo of his cousin during the commencement exercises.…