Can I use a single crystal oscillator for multiple ICs?
The ATMega328 has a full-swing oscillator, with rail-to-rail swing on the XTAL2 output. Buffer it with a 74HC1G14 Schmitt-trigger, and you have a clock you can distribute to the other controllers. The Schmitt-trigger has an input capacitance of typically 1.5 pF, so you may want to subtract that from the oscillator's load capacitance.  

This clock can drive the XTAL1 inputs of the other devices directly. I would suggest to keep connections as short as possible, because they will cause a lot of radiation. You can limit that by using an RC filter at the Schmitt-trigger's output. A 100 \$\Omega\$ resistor plus a 15 pF capacitor give you a cutoff frequency of 100 MHz.  

Don't forget to program the CKSEL fuses on the other devices to "0000".