Two voltage rails from one photovoltaic system
There are situations where that set-up works just as well as connecting only 12V or only 24V motors.

That said, it's not a great idea for reliability to connect motors directly to PVs, so "just as well" is a bit of a limited qualifier there. If the pumping system needs to work some of the time and the motors are sturdy in the sense that they can handle any voltage for longer periods of time, all you need to do is make sure the bottom PV can handle the total drain of both motors.

If you want more reliability it's better to put the panels to work together, connect them to a box that converts a wider range of voltages and currents to a stable 24V and 12V or turns off when it can't any more. For best lower-light  performance look for one with a term similar to "Maximum Power Point Tracking", but after an engineering and marketing department that's likely to cost 5 times as much (the chips for it are quite affordable now, though).

So it's a bit dependant on what you want to happen in all cases. The trouble is, a PV isn't an absolutely guaranteed supply. And I couldn't even tell you whether your specific manufacturer or reseller says 12V for its peak open voltage, or for its optimum voltage, or because it can charge a 12V car battery with 14V optimum voltage. I assume you do know, or actually hope you do.

One certainty is that without any regulation there will always be a point where the 12V motor will use all that the bottom panel can supply, then the added strain of the 24V one will make the bottom one sink to a situation where the 12V uses little enough to let the 24V one operate as well. (And some motors might have you end up at both not running, but getting hot.) 

Whether this is all day except for one hour of high sun or it is only 15 minutes at dawn and dusk depends entirely on the specifications of the motors and what the insolation is like over there in Nova Scotia. 

((A solar panel just converts the light that falls on it with efficiency X. I don't know if there's rules as to whether a manufacturer should define the power output at earth-average, or if they can just do it right on the equator.))

If they are 5W motors, then the tiny bit of time that the panels supply more than nothing, but less than 5W will be so short they can't even overheat if they want to. But somehow, I doubt that's the case.