blackstone group inc is buying 66 multifamily properties in the san diego area for more than 1 billion and plans to invest some 100 million to improve the properties whose apartments currently provide lowcost housing to thousands of people the deal would transfer about 5800 apartments to blackstone’s realestate portfolio from the conrad prebys foundation named for the developer who assembled the portfolio of properties involved the san diego uniontribune which earlier reported on the deal said blackstone already