Deducting Business Travel Connected to Personal Trip

[Adam Barr]

I live/work in Honolulu, HI, but I own a single-family rental in Newport News, VA. The property is near to extended family, and I want to kill two birds with one stone later this year and visit the property (for the first time in 18mos) as well as see family around the holidays. The property is under management, but I have a few things I'd like to check on personally.
I want to get a clearer idea of what travel expenses I can write off, but I don't want to get into a gray area of risky tax practices, so here's my question: If I'm in town for a week, can I treat the first three days as a work trip and the rest as personal time, and write of the airfare and business costs with confidence that I'm not muddying the waters? Do I need to establish certain facts or circumstances to make sure the facts are clear in the event of an audit later?