How to use two timers for one interrupt vector on avr?
ISR_ALIASOF() in the ISR attributes will let you reuse one ISR for another interrupt.

ISR(TIMER2_COMPA_vect, ISR_ALIASOF(TIMER1_COMPA_vect));


You can tell which timer triggered the ISR by examining the appropriate OCFnx bits in TIFRn.