How to make a DC to DC step up with multiple isolated outputs?
This answer is based on a reading of this specification, which implies 10 nominally 50v fixed outputs. 


Vin: 8 V DC from LiPo battery.  
Number of isolated outputs: 10  
Vout: 50 V, 10 mV ripple max.  
Iout: 50 mA per output  


As the outputs need to be isolated from each other, you need at least one transformer. 

As the input is unregulated, you need a method of regulation, so a flyback transformer seems a reasonable first thing to try.

You have no specification for how accurate the output voltages should be, and whether changing the load on one output is allowed to affect the voltage on another.

Assuming the output voltage is loose tolerance and are allowed to affect one another, then a flyback with one input winding and 10 isolated output windings would seem to be the obvious way to go. Each output would be individually rectified and filtered. Ripple would be taken care of by having a sufficiently high frequency, and large enough output filter capacitors. Feedback for voltage control could be taken from an 11th winding, or via optocouplers from one or more outputs. Of course the cross regulation will be poor.

If all outputs need to be independently accurate, you either need some further regulation on each of the outputs of a multi-secondary transformer (it need not be much, perhaps an LDO on each, controlling the transformer output to just meet the minimum dropout), or simply go for 10 isolated converters.

Multiple isolated converters has a 'fail soft' characteristic, that if one fails the others can keep going. Could this be important in your application?

There's little saving to be had in ganging the transformer should any or all of the outputs need to be independently variable over a wide range, so the only sensible solution for that is 10 isolated setup up controllable converters.