Just a step behind him, Alexander was perfectly positioned to make the switch and take the weight of the little boy instead. He wasn't a large, or overly strong man, but he'd carried plenty of grown men across the battlefields. An injured child he could manage.
"Sure," he responded simply, not wanting to say anything much more without earshot of Sirius. They'd want to get a proper look at the arm before he took to his bed. They might have to force it into position and wrap it, he knew that much from the army. It wouldn't be pleasant, so hopefully Black had something pretty damn potent to give him.
He carried Sirius into the drawing room, and very carefully lay him down on the sofa. "There now, you're alright. Your uncle is going to get you something for the pain, and you'll take it easy for a while, that's all," he told him gently, as he would for his own son.
Philip returned with the blanket, looking a little pale and shaken up. Alexander gave him a smile of encouragement, and took the blanket from him to carefully place on top of Sirius, covering the arm like Black had requested.
"Are you okay?" Philip asked softly. Alexander took a seat, and nodded for Philip to join him. They'd make it all very calm and normal, nothing to panic about at all.