A restaurant would very unlikely be hit by estate tax. For one, it's the VALUE of the restaurant, not the revenue. What do you think the value of a restaurant typically is (especially a family one like you describe) -- probably less than 500k -- certainly no more than a million [1]. Restaurants are a fine way of distributing income to a family who work there, but the value is based on profit after that.

You could own 5 restaurants of that size and not pay estate tax.

[1] http://sellingrestaurants.com/news/how-much-is-a-restaurant-...