PPR and ownership

I would appreciate any help on this one.

H & W bought a house in 1992 for £50,000 and it was their OMR.  They then sold it to H's sister for £50,000 in 1998 and it was her OMR.  In 2002, the sister sold it back to H & W for £50,000.  H & W initially had every intention to live there but their self-employed business was 40 miles away and so they decided to rent somewhere to live closer to the business and let out the house.  In 2011, H & W sold their business but had to wait for the tenant to move out in 2012.  They are in the process of moving back into the house but are looking to move in a year's time to be near their aging parents. 

Current market value is £180,000

Market value in 2002 £100,000

My questions are:-

1. Do I count the period of occupation from 2002 or 1992? 

2. I assume that I can include the last 3 years of ownership but please correct me if I am wrong.

3.  Letting relief will be available because it will be their OMR, even though it was only their actual OMR for the last year of ownership.

4.  Can I include 3 years of ownership for any reasons plus 4 years of ownership for business purposes?  I am hesitately because the legislation says actual occupation before and after period of absense.  Can I count the period between 1992-1998 as before the period of absence?

Thank you in advance