Are you putting your fingers on top of each other? In you code you putting fingers into same place (e.g. x = 100, y = 100 ) = one finger.
If you want to put 3 fingers on some element - you need provide 3 different coordinates.
thus your code should be something like:
int x = driver.findElement(MobileBy.id("id1")).getLocation().getX();
int y = driver.findElement(MobileBy.id("id1")).getLocation().getY();
MultiTouchAction multiTouch = new MultiTouchAction(driver);
TouchAction action1 = new TouchAction(driver);
TouchAction action2 = new TouchAction(driver);
TouchAction action3 = new TouchAction(driver);
action1.press(x+2,y+2).waitAction(3500).release(); //3.5sec for sure, 2 pixels inside el
action2.press(x+4,y+4).waitAction(3500).release(); //3.5sec for sure, 4 pixels inside el
action3.press(x+6,y+6).waitAction(3500).release(); //3.5sec for sure, 6 pixels inside el
multiTouch.add(action1).add(action2).add(action3).perform();