Not oysters. Gills aren’t decurrent enough.

Definitely not oysters. Possibly Tapinella atrotomentosa.

In my experience, the only way to “really know” a mushroom is to find it repeatedly, have it in your hand, smell it, and have someone next to you who really knows their stuff and talk to them about the mushroom in your hand, and learn that way what characteristics to look for. Then find it again, identify it yourself, confirm with an expert. Repeat until you don’t have to ask.

Pretty much the only way to be 100% certain about any mushroom, after narrowing down identity visually, is to do a spore print.