You Can hook up 2 chips to one crystal. You have to leave the Xtal2 pin open on the 2nd chip and drive the xtal1 pin from xtal2 of the first chip.
I was trying to do this but couldn't get the fuses right. Eventually decided 2 crystals were easier, both chips could be loaded with standard bootloaders/fuse settings.
9.4 Full Swing Crystal Oscillator
Pins XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier which can be configured for use
as an On-chip Oscillator, as shown in Figure 9-2 on page 28. Either a quartz crystal or a ceramic resonator may be
used.
This Crystal Oscillator is a full swing oscillator, with rail-to-rail swing on the XTAL2 output. This is useful for driving
other clock inputs and in noisy environments. The current consumption is higher than the ”Low Power Crystal
Oscillator” on page 28. Note that the Full Swing Crystal Oscillator will only operate for VCC = 2.7 - 5.5 volts.
Here's the board I ended up with. Bare boards available for $5 mailed to your US location.
