1 set of resistors is probably adequate, however, the value of the Rs will be determined
by how many devices are on the buss, and how long the wires are. This is because all those
devices and longer wires increase the total capacitance on the buss, so the risetimes of
the signals will increase [simple first-order RC charging]. If this gets too long, buss
operation will become irratic.
Whereas you usually see 4.7K - 10K pullup values mentioned, 2.7K is probably a better
choice for the situation mentioned above.