It sounds like the job should be pretty simple. The mechanics of household electrical are very straightforward. I would definitely lean on your BIL here: discuss the project, not just what to do and pitfalls to avoid, but also have him give a vibe check on your understanding. He knows you better than any of us do.
I've got three meetings and an unscheduled emergency requiring 90% of the IT staff to sit on a conference call that says you'll be staying late Friday, too.
Best I can give you is resigned condescension.