Put two dotted sixteenths in 3:6y tuplets inside a 12:8y tuplet before applying a two strokes multi-note tremolo. Then hide the inner tuplet numbers and the outer tuplet bracket:
Put two dotted sixteenths in 3:6y tuplets inside a 12:8y tuplet before applying a two strokes multi-note tremolo. Then hide the inner tuplet numbers and the outer tuplet bracket: