When do you say two clocks are asynchronous?
can we say that clocks C2, C1 and C0 are synchronous


Yes. The whole point of a PLL is to "lock" one frequency to another (phase, actually, but it turns out to fix the frequency too). They could be asynchronous if the PLLs are malfunctioning, in which case the output from the PLL could be a free-running clock (worst case).

Two clocks are asynchronous if they do not depend on each other, for example two free-standing oscillators at the exact same frequency will still be asynchronous, since you will always have a small amount of drift and an unknown phase at startup.