Percy didn't mean to stand up straighter, and make himself look important; it was a defensive habit, especially one he had employed when living at home or being involved in a large family gathering. George's arrival changed the dynamics of things, and what went from a one on one conversation now shifted to an two against one potential. Percy stood his ground, trying to show that he was not daunted by not one, but two Weasley brothers and looked over as casually as he could at George.
"Happy Christmas, George. And yes, if you have food, I can manage to make us something. Or we can order out. But can we please get up to your flat so that we can discuss this openly? I don't fancy getting pinched before I've done a blessed thing yet, right?" and he turned to look at Fred, "It is of a private nature, but am I mistaken? Do you not have an inkling what I may be here to coordinate with you two?"
He felt a pang of nervousness, and determined not to show it, he squared his shoulders and turned to look at George, "I wouldn't be shutting your shop down. I happen to fancy this shop, as much as you may be under an adverse impression. Your place is....," and he glanced from George to Fred and back to George. His expression shifted, and he was candid with his words, "This place is brilliant, utterly fantastic. And Mum and Dad should be exceedingly proud of you, as should all of us."
He let those words sound as they may; he was very proud of them, for their adventurous spirit and instinctive business knowledge. There was no envy in his tone, only true pride.