Lots of good questions about brooding. I have gone solely to broody hatching for the last 7 years using a variety of hens, including Silkies, because of the ease and success. I've hatched in designated broody hutches and in the main flock (depends on hen, depends on flock).
The answers depend a lot on your set up and a lot on your broody's temperament and your flock's temperament.
First, her location. If she is safe and out of foot traffic of the other 2, and her nest is safe, and the other 2 are calm tempered, she can stay where she is to hatch. Troubles only come if the other hen(s) try to lay eggs in the nest disturbing her and the eggs (pushing her or the eggs out) or they want to sit and roost with her in the nest (typically they will sleep on the roost at night). If she stays in the main coop, you should use a felt pen to mark the eggs in case a new one is laid. I mark them with the date set since I tend to forget. All eggs should be set at the same time so the hatches are not staggered (it throws the hen off if some chicks hatch while others are still developing...typically she abandons those not yet hatched or stays and ignores those hatched).
Note when she began to sit on the eggs to anticipate chicks in about 21 days. She will sit faithfully 24x7 for 3 weeks (give or take a day) getting up only to eat, drink, and poo generally for 20 minutes once a day. She should be able to get easily to food and water to do so, and she should be able to get back to her nest easily without confusing where it is. (If any of that goes awry, she needs a separate brooding crate with bedding and with food, water close by, but not tippable into the nest, and a little area to poo).
It is often desirable to "candle" the eggs about 7 days after setting and again at 14 days to make sure they are developing. You have plenty of time to reset eggs as most hens will brood up to 5 weeks, especially Silkies, or until they get chicks. Obviously you don't want her to brood too long, as she can lose a lot of weight during the process, so checking at day 5 or 7 will give you an idea if they are growing chicks. You'll see a roadmap of veins. Just use a strong LED flashlight, shine up through the "fat" end of the egg while holding in one hand, in a dark area. You can candle again at day 14 just to make sure. By then you often get a dark blob on one end with some veins outreaching. Do not disturb nest from day 18 to 21 as that is "lock down" when the chicks get into position for hatching.
Once the chicks hatch, they stay with mom. Troubles only arise if your run has gaps or holes that chicks can strand themselves away from mom with a "stupid chick trick." ...Or if the other chickens cause problems and attack the chicks (most mellow flocks are fine with the chicks, and mom is very protective). My rooster is very protective of the chicks as well. The other hens simply ignore them. But you will have to be watchful until you observe how the others are doing with the chicks. Silkies generally make great moms and can be something of a diva with their chicks.
As to weather. I've hatched in all seasons, including dead of winter (stubborn Silkies...ice-snow storm middle of January, in low 20's, wind chill in low teens). Amazingly the little chicks do fine as long as they are out of direct weather (covered run, enclosed hutch). They run around in their little down jackets using momma as a warming hutch when needed. No heat other than momma is needed. Mom will sit with the chicks tucked under her for the first 2 days after hatch (they have enough food source from the absorbed yolk as they dry and gain strength), then she will lead them to food and water. Make sure that all are on the chick crumble and the water set up is such that a chick cannot get to it and drown (normal waterers with the gravity flow into a shallow bottom pan are fine, dog bowls are not, water nipples can be problematic depending on chick). Problems only arise if chicks can't make it up the ramp to the main coop. Momma will take up residence in the run, or wherever, not always an ideal safe place. I have a side coop that I use for more timid brooders that is large enough for momma and chicks the first week or two and the chicks don't have to navigate the ramp until they can fly (about 2 weeks).
If main run is not ideal for chicks, but coop is fine for hatching, momma will follow chicks happily anywhere after they hatch. Wait until they dry off and are fluffy before moving them with momma to your desired location. Moving momma with eggs is trickier. Some hens bond to the EXACT location they started the brood and will reject any other nest. Some hens will plop down on eggs wherever. If you do try to move with eggs, stand by and see if the hen is happy, check an hour later. I've had hens reject moves altogether to return to their first nest. It's generally better to settle a broody hen on a desired nest first, then give her eggs, rather than try to move her after she has settled on eggs.
That should get you started. Feel free to ask other questions if needed.
Lady of McCamley
