I was going thru ISO1540 datasheet. In Fig 6 (page 10), the I2C bus has pullup resistors at each slave device. One master and 3 slaves, so 4 pairs of pull up resistors.
I2C bus needs only one pair of pull up resistors per bus.
1540 datasheet -
http://www.ti.com/lit/ds/symlink/iso1540.pdf