Applying Single Table Inheritance
Unless I'm misunderstanding your requirements, the Person, Individual, Company, and User tables could be combined into a single record since the relationships between these tables are all one-to-one.  Unless this is some kind of trick question...

One could go so far as to say all the tables that involve one-to-one relationships could be combined into a single table since that would eliminate the duplicate foreign keys, thereby saving space.  Having said that you'd really have to be hard pressed for space to worry about saving that small an amount of space.

It looks to me like you need to revisit your design spec with an eye for simplification.