Severus saw Al's bemused frown, and hit the note with his usual barrage of detection charms. It's genuine, all right. He muttered the words under his breath, speaking out of stubborn hope, even as he firewrote so that Al could see. As his wand flicked in midair, his gaze flicked rapidly across the parchment.
Al's bemused expression was apparently contagious.
"Huh," he snorted, his wand firewriting ceaselessly as he spoke, in a process which was rapidly becoming a reflex. I can see the need for two weddings, if only to redress the wrong of Riddle's annulments, he grumbled, but three strikes me as a flagrant bid for more of the spotlight, more wedding presents, or both.
He's your brother, Severus concluded with shamelessly obvious relief as he handed the letter back, no doubt he expects you to be the one to reply.