I just wanted to add that if your son acted like an adult he'd fucking talk to you about it first.

If my son treated his snooping on my will like that I'd tell him he doesn't have to get anything if he won't let me explain the situation to him.

An almost 30 year old should be able to talk to their parents FFS - "Hey dad, I was just curious, is there a reason you split the house between my younger brothers? Did I do something to upset you?"

"Of course not son - I was just concerned about your mother trying to use your relationship to interfere with the business side of things."

"Dad, I would of course not do anything to mess things up for our business - it's yours and ours - mom didn't have anything to do with it."

But this whole storming and cursing dad/step mom out - grow the hell up.