I prefer to use frozen fruit for this smoothie because it helps the smoothie have a nice, thick and creamy texture. I also find it convenient to just grab prepped fruit from the freezer without having to worry about whether it's ripe or not. That being said, you can definitely substitute either fresh banana or pineapple if you like. The smoothie will be thinner, so you may wish to start with less milk at first and add more as needed to get the desired texture. I would probably not add both fresh banana and pineapple, but instead one or the other, since I find the smoothie's texture really does benefit from having at least some frozen fruit.