You may be dealing with a clutch size issue with the silkie. Give her a little more time. Silkies will sometimes go broody on a smaller number of eggs but younger well fed females may go longer. The bantam is outside my experience.
I have an austa white hen and I don't know if she is broody.she lays and sits on the egg for around two hours but leaves it and returns some times a few hours later.she will leave the egg if I enter.we had a rooster about a week ago who I think managed to ferterlise the eggs but not totally sure.is she broody I took the egg away when she left but she started again the next day.is she broody and how do I know if egg Is fertile.
Ps I hope this was the right place to post this