"I'm sorry," Percy's apology was an automatic reflex, picking up on Molly's frustration and feeling bad that he'd brought up the subject. Unfortunately, he knew the conversation wasn't going to get much better, since the main reason he'd come was to finally tell his mum about what happened between him and the rest of the family in her future.
Even the mention of Fred and his father caused Percy to grimace for the parts they played in his life. But it was short lived, for Percy immediately covered it over with a thoughtful question, "I wonder how father would react to being here. I imagine he'd be in bliss, surrounded by all these Muggles without restriction from the Ministry. He can't be that far behind." Mum must've missed Arthur most of all so that went without saying. As for his brother, "And it would be good to see Fred, after all this time..." he cut himself off to cast a nervous look at his mother. Did she know Fred had died, or would this also be a surprise for her?