Hmm, I'll have to figure out how to weigh them. I'll try to get back to you on that. School starts tomorrow, so things are about to get hectic. Karen and Carrie are our two most skittish birds, so I might have to try and move them to level ground to weigh myself holding them.
Having never seen full grown bantams in person, it's hard to gauge, but I would say my girls are definitely larger than half the size of the others.
If you have a scale that will weigh accurately in the right range, a towel or a bucket & lid can be your friend. Wrap the bird in the towel and lay it down on the scale, or put the bird in the bucket and sit the lid gently on top. Either weigh the extra thing first and zero (tare) the scale, or weigh it separately and subtract it from the weight with bird.
Hmm... I hadn't thought about identifying who was responsible for which egg, but I don't think any of the other girls should be producing green or blue, so I might be able to figure it out by process of elimination. Might have to come up with a creative camera setup to do this. My battery powered wireless cams aren't meant for continuous footage.
Process of elimination will usually work nicely.
Since they are just reaching laying age, you might try checking their butts on occasion.
https://www.backyardchickens.com/articles/who-is-laying-and-who-is-not-butt-check.73309/
Check the male first: you know he is not laying. (vent small, puckered, dry-looking, and you can feel the tips of two bones just below the vent, close together.)
Then start checking the females with the biggest reddest combs. A layer's vent will be larger, less puckered, look moist, and those two bone tips will be lower down and further apart. A pullet getting close to laying will show some of the signs of a layer.
You can probably rule out at least half the pullets at this time (definite non-layers), which leaves fewer birds that could have laid the first egg.
Over time, you can probably work out most of the egg colors just from who starts laying around the time you start getting a given color of egg. It can also be fun to know who started laying how soon. (Do the "fast maturing" breeds actually start laying sooner? Often yes, but sometimes no.)
If you happen to catch one in the act of laying, of course that will give you a definitive answer for her.
Once they are laying, you can put just one or two birds in a separate pen until they lay eggs (usually a day or two), and you will know what color eggs they lay. The "separate pen" can be a dog crate, or your little prefab coop, or something of the sort. Just one bird will tell you exactly what egg she laid, but if you know the egg color of one bird you can put her with another one, which lets you check the unknown without having her alone & lonesome all day. Or if you put 2 birds in one pen and you get two brown eggs, of course you know that they both lay brown.
Cameras might work too, but I have no personal experience there.