This is great fun -- humorous and verging on crackiness, yet it's believable in a really-skewed-wizard-world way. There's enough of a serious edge. I enjoy this sort of clever parody of the marriage-act trope.
As you present them, Abraxas and Percy are so well-suited. I can just hear them, negotiating and analyzing in this spot-on tone of understated matter-of-factness. Percy's getting off on the financial news is hilarious (and I love that he's no walk-over; he's a match for Abraxas). Abraxas himself is great, with his wryness and his "purebloods are never flustered" unflappable demeanor.
"Marriage Acts" -- clever double-entendre.
Lines I liked:
Abraxas' words were coated with enough frost to cover Siberia.
"Various rewards for good behaviour." Lucius admired his fingernails.
Abraxas saw no reason to not look his best even if he was going to be among blood traitors and half bloods, not to mention Mudbloods.
"No, just relieving a few kinks in my back. His bed is too small." "Stop. Right. There." Lucius held up a hand. The whole Lucius-Abraxas relationship is well-done.
Nothing in his previous marriage had prepared him for an irate person throwing lead crystal at him. Haha! The fight scene is really funny, with Abraxas calmly dodging decanters like a choreographed ballet.
Yeah, I think Percy and Abraxas are going to make this work.