Christine Davis Special to the Daily News As Mark and Jean Cohen will corroborate, it’s nice to have an architect as a relative when it comes time to renovate your home. In 2009, when they bought their penthouse condominium on the South End, they fell in love with the view, but they knew they would have to tackle a redo. And that’s when they called upon New York City-based William Cohen, Mark’s cousin, for help to customize the condo, No. 7HII at Atriums, 3400 S. Ocean Blvd. Additionally, they hired Joseph Black, owner of the Jupiter firm, Omega Builders, as the contractor.