Feeding can be a bit difficult, especially if your betta is a little piggy. I would suggest feeding your shrimps once a day, perhaps when you feed your betta.
Since ghosts are carnivorous, they can eat the same thing your betta does. If you feed pellets, just soak one or two extra. When you feed your betta, feed him in one corner of the tank, and while he's distracted, go ahead and squeeze the pellets and put them in the opposite corner or somewhere where he won't find them once they've sunk. They should sink to the bottom for the shrimps to find. If your betta starts going after the sinking pellets, redirect his attention by hovering your hand right in front of him as if you were to feed him, then moving it back to the corner.