i usually candled them once a week, since it only takes three weeks. At this stage, you should be able to see blood vein type things, and perhaps some solid. At two weeks, you should be able to make out a solid shape and some slight movement and at three weeks check for peeping inside the shell.
Good luck!!

I candled yesterday and found an embryo! But only one out of 8 eggs, distinctively. The others seemed like they just had yolks floating around. Some of the eggs I put there a few days after the others, so I will give them a few more days. I really had hoped to get 3 or 4 hatched this year. Should I wait until the embryo hatches (if it does), and then put down more eggs? Will mamma still be broody...or raising a chick? Should I put down more suspected fertile eggs now, or is it too late? How does this work?

If you put down more eggs now, it is likely even if they are good eggs, the hen will think they are not since they didn't hatch with the others, you could then put them in an incubator and then hope the hen will take to the babies, otherwise you will be raising them in a box. I have done this before, and trust me, unless you have a good protected place indoors that is also well ventilated, you will wish to goodness they are outside. I wouldn't put any more down now.

Don't put any more under the hen. She will leave her nest when the 1st ones are a couple of days old and the rest will die in the shell. Staggered hatching doesn't work unless you take the 1st eggs that are due to hatch out a day or so before they hatch. Then you have to put them in an incubator to hatch and keep them in a brooder afterwards.

You might want to buy a good book on raising chickens. They come in handy as a resource when you need it.
M

I'm going to disagree here...

There's two hens, one chick. There's probably going to be one hen AT LEAST that is going to remain on the eggs anyway, or some nasty fighting that could result with "no chick". I'd go for it. You may have other broodies by then anyway. Silkies are so notorious for being broody constantly. I think it's worth trying...but that's just me! I'd do it...

Suzie