A spice bag means in a cheese cloth pouch, referred to as a Sachet in french (which is the traditional), it is similar to a bouquet garni ( herbs and spices in a cheesecloth pouch). As for the garlic, it is probably preferable to use fresh (or frozen cubes) simply because fresh vs dried always gives a different flavour, in the sense that dried herbs are more intense, therefor you need less. I would try it both ways and see if your family can taste a difference.