Form 1065 - Commercial Rental

I (husband & wife) have an LLC which owns a commercial building.  The building is rented out all year long.  1/3 of the building is rented by a individual person.  2/3 is rented by my sons' LLC (automotive business) or which my husband and I are 20% owners.   The son's LLC pays rent to use the building, but has been known to skip a month when funds are low.  Question:  Does son's LLC count as personal usage since we own 20% of his busines?  If so, how do I allocate expenses across the rented vs personal usage?  Would items like depreciation only be deducted on a percentage base, i.e. 1/3 of the yearly depreciation?