Thank all of you for the responses! Those videos are so cool, haha!

Una is doing well. She is still spending most of her time sitting down, BUT she has been practicing standing and hopping. This morning I saw her standing quite well for at least 10 seconds with no wobbling at all, and then she took a couple very neat hops before choosing a place to sit! She doesn't usually manage so well yet, but I'm seeing instances like that more and more. She is growing as fast as Gloria, both of their wings and tiny tail feathers are coming in nicely -white for Gloria, and a mothlike blue roan color for Una. If I could figure out how to post images I'd show you.  Thanks again!

Thanks for the tip, Holly! Super helpful!

I am pleased to announce that Una is making tremendous progress. For the last day or so, I have even seen some "unnecessary standing", i.e. standing that was not necessary to get a drink, move closer to the light, etc. I've seen her standing up while eating (for brief intervals) and even standing and scratching her head with her stump! 

She is somewhat nervous about being held, I think because it makes her feel unsteady and she flutters her little moth wings like crazy until she can get settled. Gloria (her buddy) is a big ham for attention and will. Not. Get off my hand voluntarily.

We rehomed the other 5 chicks today because we don't really have room for them when they grow up, plus their mom was threatening to kill my toy poodle whenever he stepped out to pee, lol. But it means I can now focus more on these two.

Here are the pics:

1) Gloria & Una's "family photo" at 4 days old. Una's the one sitting down, duh.

2) Una's legs. Can't see it too well here but she has 3 tiny toes with claws, 1 is at a right angle to her body and 2 point backwards and are fused together. Her stump is growing as fast as her other leg and seems healthy, except for some bruising from when she was still trying to walk on it.

3) Una today (about 10 days old). Their wing feathers, tail feathers and coverts are coming in nicely. She was trying to dustbathe, because of the patterns on my quilts looking like dirt I guess. 

4) Una standing! It's tricky getting pics of her standing, this is actually the first one I've gotten where you can tell. She and Gloria are about the same size, but Gloria was coming over to check out my phone, so she looks bigger. Una's leg rests in a neutral position when she's just standing and thrusts backwards for balance when she hops. She also uses her wings for balance.

Thanks for being interested! I think everyone I know is sick of me yapping about her, haha. Yesterday I was celebrating the new accomplishment of pooping standing up, which is really great for hygiene purposes but seems like a very strange thing to get excited about! And thanks again for the tip about the pictures!

Una is still doing great. She stands up quite often now, although she has a tendency to stumble sideways. Do other tripawd animals have that problem, I wonder? Probably. Anyway, I'm letting her practice standing & walking outside the brooder, places where she can't just go lean on the wall. Her one leg is already more muscular than Gloria's two.

Also, we finally got a good picture of her standing up! 

Her legs have darkened up to olive green, which kind of helps me narrow down who her dad was. I think there were at least 2 others with the same sire in the clutch, though, so I don't think it's genetic. Probably the egg didn't get turned properly or there was a temperature fluctuation...7 eggs was probably too much for a first time mom. But I've had smaller hens hatch 16 "perfect" babies before! Now I'm just rambling. She was perfect enough to hatch by herself, and that's a tough job.

Anyway, Una's gotten really good at standing and actually seems to prefer it to sitting down, though she still sits more than Gloria does. She "vibrates" her stump leg just a little when standing still, for balance (that's why it's blurry in the pic), and uses it as a rudder when she hops. She's also starting to like being held more. Now both cry for someone to get them out of the brooder. The danger of keeping chicks in the house is that they will never let you do anything else! (I'm typing this with them on my lap.)