You're blessed to be able to recover under the watchful eye of your, BIL, a trauma surgeon.
Honestly...I find the living situation you will return to concerning. Without seeing the two staircases you need to navigate, imagining that they lead to an attic makes it sound very challenging and potentially unsafe. You're going to be dealing with a degree of pain, weakness and compromised mobility.
Wondering if there is a bathroom in the attic, or will residing in the attic necessitate multiple trips up and down throughout the day and night? If so, you'll definitely need a bedside commode. If it's an older home, I am imagining narrow steep staircases.
I am wondering whether your sister or BIL are willing to assist you going up and down early on. If you've mentioned this to your surgeon, wondering about his thoughts. Is there anyone else you can stay with for the first couple of weeks, at least, or is some type of transitional care a possibility for the first couple of weeks?
If you're able to provide a better description of the living conditions, more detail on the staircases, whether there is a bathroom or kitchen in the attic etc, we'll be able to better advise.
Hope to her from you soon!
@ACIM