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This Sparfun Block SparkFun Block for Intel Edison - ADC - DEV-13770 - SparkFun Electronics , won't let you connect 3 sensors through I2C, this block allows you only to connect up to 4 Analog devices like a potentiometer. If you are interested in connecting several devices through I2C I would recommend to use an I2C Multiplexer.
Hope this helps, have a nice day!