For your 600D, the most generally useful addition from your list is a fast normal lens, especially a 35mm, because APS-C makes 50mm and 85mm behave tighter than they would on full frame.

A 35mm is better suited to family portraits and indoor party/wedding coverage where you often can’t step back. A 50mm can work, but on your camera it’s tighter and less flexible indoors. An 85mm or 100mm is even more restrictive for groups and small spaces.

Why the 70-200mm recommendation? It’s popular for weddings because it gives strong subject isolation, flattering perspective, and reach for candid moments. But indoors, especially on a crop body, it can be too long unless you have lots of room. The f/2.8 version is much more suitable in low light than the f/4, but a fast prime still has an advantage for dim indoor shooting.

Also, don’t rush to buy based only on lists. Your current lenses already cover many situations; spend time learning what focal lengths you actually use most, then choose the lens that fills that real gap.