Question about Query or synopsis

The way I understand it, you only need to show your MC in a query.

A synopsis is a little different because you must tell the entire story...so if those secondary characters have a major role in what happens to your MC then I suppose they would need to be included too.

In your Query letter you're restricted by space and the necessity to grab the Agent's attention very quickly with what and whom your story is about. Who's the protagonist and what's his predicament? Enough to whet the Agent's interest sufficiently for him to move on to stage 2 and read/ask for the synopsis/manuscript. A couple of paragraphs, maybe, doesn't give much scope for other than stating the setting, the protagonist, and his predicament.

The synopsis reveals how the main plot unfolds and how the story concludes but bit players and subplots don't need to be included...unless anyone else wishes to advise differently.

Querry should contain your Main Character, Antagonist, Conflict, and what your MC is going to do to overcome the conflict.

Synopsis keep it down to as few characters as possible. Filler people needn't be mentioned at all.