how to grind pistachio nuts so that they stay dry

The more liquid texture is a result of the oils in the nut being released as it is crushed. To avoid releasing the oil, start with cold nuts and shred or grate rather than crushing. Any kind of blunt trauma will squeeze the oil from the nut, making it gloppy. Keeping the nuts cold will cause the oil to solidify, keeping the final product fluffy.

I have had some luck with other oily nuts by grinding them down into semi-large pieces, and then letting them dry out on a flat cookie sheet. Then, step-wise, grind iteratively, with dry steps in between. If you can do this one time with a lot of product, you can save some in an air tight container for next time.

I would suggest investing in a proper nut grinder. Despite the name, these actually grate, rather than grind, the nuts, and thus give you the flour-like texture you want in a pretty foolproof way. In a pinch, a hand-held rotary cheese grater can be used, but your hands will get pretty tired.

When grinding almonds I first blanch them in hot water, then spread out thinly on a baking tray & allow them to dry out in the oven at 90 C for at least 30 minutes. When they are completely cold they can be finely ground to a flour & used for making marzipan. This is the only way I have found to make it successfully. I make marzipan in 1kg quantities for my Easter Simnel cake & also for making marzipan figures.

I think you should remove the oil from pistachio. Actually I'm trying to make pistachio macaron. And I have Kirkland salted pistachio. If I grind it straight from the packet then it'll become pistachio paste which I definitely don't want. So I'm trying to remove excessive oil from it. To do it I have to boil the pistachio few minutes then dry it in the oven. I'll give it a try. If it works then I'll write about the outcome ok?