Cascade multiple Full-bridge Rectifiers Connected to Multiple AC Sources
Observations:


With the bridge rectifiers in series, if (say) V2 was quite active and (say) V1 was close to zero volts, the DC output would be 4 diode drops down on the AC voltage and this is worse than just collecting energy from V2 and its bridge rectifier.
Having the bridge outputs in parallel means you always collect "decent" energy even if only 1 source is active but, the down side is that you only collect energy from 1 source (that source being the one with the largest amplitude).
If the receive coils are individually resonant tuned (using parallel capacitors) then you might consider having all receive windings in series and one parallel tuning capacitor.


I would urge you to do simulations as this will tell you a lot and, the number of scenarios that can be tested will prove to be a better source of what you need to know than my limited set of observations. If this was my project, I'd be simulating it to death because IT WILL provide decent and real-world repeatable results.