26MHz crystal not oscillating - strange capacitor behavior
I observe a constant 2.4V at OSCP and GND at OSCN [VDD for U1, which
  is an RF transceiver, is 3.3V]


Most integrated external crystal oscillator circuits look something like this (example is from a PIC32MX MCU):-



An unbuffered CMOS inverter is used an amplifier, with a high value feedback resistor (Rf and/or Rp) biasing the inverter into its linear region somewhere between GND and Vcc. Due to the negative feedback, both input and output voltages should be the same (at least when the circuit is not oscillating). 

The fact that your input and output voltages are wildly different suggests that either the feedback resistor is not present, the oscillator is not enabled, OSCN is shorted to ground, or the IC is damaged.