Capital gains on sale of residential property

I have a few queries regarding capital gains arising from sale of residential property: 1. Can the assesse purchase a commercial property from the sale proceeds arising out of sale of a residential property? If yes then how much benefit can be claimed? 2. How will the capital gains be assessed in case of joint ownership of the property? 3. In case of joint ownership, how can the investments be made (in property or bonds) and how much? 4 For claiming the cost of improvements, are the supporting bills required? (since the repairs and improvements were carried out over the tenure of ownership, how is it possible to produce the bills)? 5. In case where the purchase agreement mentions that 2 adjacent houses were purchased and practically the houses are joined and is now a single flat? Can it be treated as a single residential property for sale?