Celine Dion is looking healthy and happy with her family by her side. The legendary singer took to Instagram on Friday to share an update on her ongoing battle with Stiff Person Syndrome, a rare neurological disorder that causes muscle stiffness and painful spasms, RadarOnline.com can report. Dion, 55, opened up about her condition alongside a sweet photo of her and her three sons, Rene-Charles, 23, and twins Nelson and Eddy, 13, smiling atop a podium for indoor go-kart racing company K1 Speed. She shares all three sons with her late husband and manager, René Angélil, who died in 2016. “Today …