Clarification on section 54 of income tax act

hello

my father had 2 residential property in his name. he received them in inheritance from my grandfather. we sold 1 of the residential property in august 2013 and invested the full gain in a new residential property thus availing the benefit of section 54. now we want to sell the 2nd residential property and invest the gains from such property in a new residential property. can we do so? according to my understanding of section 54, a person cannot avail the benefit of section 54 on 2 residential properties. also further my father also owns a commercial property, from where he used to do his business. we also want to sell that commercial property and invest the gains in a new commercial property. can we do the above 2 transactions within section 54 and 54f of income tax act and if not, then what are the ways to save tax other than investing in bonds.