Nobody can observe/coach themselves, and training without coaching isn't training; it's maybe practice, and more likely plinking. Without a solid book-learning understanding of the shooting basics, nobody can be a coach, and with it, no coach can function alone, they need shooters upon whom to apply their skill.
Years ago, with our small, local Marine Corps League shooting team; we established the buddy system for shooting/coaching. Everyone became a coach, everyone became a shooter, and pairs took turns observing and coaching each other. There is no need for perfection, progress is a goal, and insisting on perfection is the key impediment to that progress. Along with the shooting, expect the coaching to improve as well; everybody starts from basics and improves from there. A good partnership will learn to trust, to discuss/negotiate how things are being done, and how they can lead to improvement. If perfection is the goal, failure is assured. If improvement is the goal, success is very likely. Nobody is right every time, all the time.
How often training takes place is less important than the quality of that training, and for practicality, frequency needs to be driven more by the economics of providing the resources, like range time, travel, targets and ammo, etc.
Training should emphasize one aspect of the basics at a time, working until improvement is seen, until that improvement satisfies the shooter they are ready to move on to another aspect. Waiting for perfection is a futile occupation and too much repetition results in boredom, frustration, and degrades interest. The training plan should rotate through the basics, and loop back to the beginning over and over. Progress is based on improvement, and improvement needs to come in stages.
There is nothing wrong with swapping out training partners, either; different viewpoints will broaden the perspective, and this can only be a good thing. Teams need to meet; good teams meet to shoot, talking is only a small pat of the program, and usually wastes good shooting time. Talk less, shoot more.
Greg