That Windows 8 is horrible is merely an opinion. Why not let your brother enjoy what he purchased, and perhaps make his own decision, instead of deciding for him that he needs to spend another chunk of money to legally use a much older OS on his new computer?
As for the laptop's compatibility with Windows 7, the other posters have pretty much covered that. If drivers exist, it's compatible. In the long run though, it's a sad waste to throw much improved, more efficient coding out the window based on an arbitrary opinion about a user interface.
I would disagree that the Windows 8.1 update makes the OS more like 7. The OS is already like 7 in functionality, however after using 8 for years, you can clearly see the performance difference between 7 and 8. The only major difference is the Start menu. In 8, it's actually, surprisingly very useful.