I would seperate them when you first bring him home, and again next week when you bring the girly home too. Your boy will be fine after the op generally speaking, albeit Sleepy probably. However, he will not smell like himself at all and his sister will likely show some aggression. Im sure you'll agree that after an op, minor or major, that he needs rest and relaxation but that probably won't happen if you don't keep them apart.
Your girl will need longer, I had to keep Pandora in my bedroom for over a week as a) she smelled differently also, b) she will have more substantial wounds afterwards than a boy and any playing/rough housing/ attempts at cleaning etc will aggravate or split open her stitches. If she's wearing a cone which she should be, she may also need help eating and drinking. The boys tend to bounce back practically immediately, but att least half of my females over the years have required assistance after their spaying. Good news is, they heal hella quick and things will be back to normal really soon.
Also, well done for being a responsible pet owner and getting them both done!