Wash the peaches well, then cut them in half and remove the pits. Place the peaches in a large food processor and pulse in short bursts until the peaches are in chunky pieces.
Remove 1/2 cup of the peaches, and add the passion fruit puree and sugar to the remaining peaches in the food processor. Blend until very smooth. Taste the mixture, and add additional sugar if desired. (The amount of sugar you'll need depends on your taste and the sweetness of your peaches.) Add the chunky peaches back to the peach puree, and stir it in.
Pour the popsicle mix into your molds and freeze for 30 minutes, until the pops have begun to set. Insert popsicle sticks into each pop, and freeze for another 2-3 hours, until frozen completely.
If you want to cover them with chocolate, combine the finely chopped chocolate and coconut oil in a bowl, and melt it in the microwave, stirring after every 30 seconds to prevent overheating. The chocolate should flow freely and be fairly thin—if it still seems thick and gloopy, add more coconut oil, a small spoonful at a time, until it's thin.
Unmold the popsicles. Hold one over the bowl of chocolate, and with a large spoon, pour chocolate over the popsicle, rotating it as you pour so that the whole thing is covered. Immediately sprinkle a big pinch of chopped pistachios on top, while the chocolate is still wet. Repeat with the remaining popsicles, until they're all covered with chocolate. Serve immediately, or keep frozen until ready to serve.
I always leave the skins on my peaches when I make these pops—they're a little chunky anyhow, so I don't mind a little extra texture, and I love the spots of color too. If you want your pops perfectly smooth, remove the peach skins by bringing a large pot of water to a boil, and cut an X through the skin on the bottom of each peach. Drop the peaches in the water for 1 minute, then drain and cool slightly. The skins should now slip right off, and you're ready to make the popsicles. This recipe yields 8 small (1/4 cup) popsicles.