You could use a single flash unit to charge them to 600 volts, you charge them in parallel, and discharge them in series. You have to be very careful though as you're starting to get into territory where the voltage can jump 1cm of air.
I have no idea what would happen if you put two such units in series, don't let them get anywhere near each other though.
Yes you can, but it might not work, ''boots'' disposable cameras are the most well built IMO, other once the voltage gets over 330v, you see smoke.
also, those capacitors cannot handle all that voltage, and exploding capacitors will make you sh!t yourself
If the units would still charge their independent capacitors without interference it wouldn't matter Amando, each isolated circuit would never be exposed to anything over it's normal operating voltage