If both filters are adequately sized for your pool and pump so you can use either, I would not recommend using both. Decide if you prefer sand or DE and use that one. BTW, you can add a little DE to a sand filter to improve its performance.

In series, you double the resistance to the pump, in parallel, you halve it, so you have do all the figuring of pressure rates, etc, which I cannot figure out for this.

If they are neither adequately sized, then I would recommend getting a properly sized filter for your pump.

Whichever you pick, you can empty, clean up and store the other as a spare.