Yup, it's hard, but it's addictive!
When you look back in a couple of years, you'll smile at what your first guesses for marbles were and how far you've come.
Not slag.
Essentially solid color though there are variations in it. If it's a little smaller than normal (closer to 9/16" than to 5/8") it would be called a "game marble". But it's closer to 5/8", isn't it. (Trying to read the tape measure.)
The glass texture together with the swirl pattern makes me think of Champion Agate for the first possible maker. With Alley Agate as a fall back choice.
Machine-made.
The marble-rounding machine which revolutionized the American marble industry was invented around 1900.
At that time, marbles were still "hand-gathered". Which meant that globs of molten glass were picked up on a piece of metal and manually dropped onto the mechanical marble rollers for rounding.
In the 1920's the molten-glob-producing process was automated. That's when the "gob feeder" was introduced to the process and marbles became entirely machine made.
With your new pix, I confidently say Vitro Tri Lite on the left. A 1930's marble. Still not sure on the right, but it does look vintage. You showed a lot of the white and not so much the yellow. I think it might turn out to be a Peltier patch.
This last one is a Vitro cage style Cat's Eye. Could be from the 60's through the 80's. If you keep marble hunting, you'll find it's a very common style.
A few dollars for the whole group? Or few dollars for an individual? I might pay a few dollars to get the big Marble King Rainbows.
Wait for a second opinion.
The left picture looks like a Vitro Conqueror. Maybe a hybrid version if the blue patch is surrounded in green.
The right picture looks a little odd ... but I guess it could be the backside of a Conqueror.