Both parents are right above them at night on tree limbs keeping watch. If you look at the other cam (long distance ) you will see them on limbs right above them.
Every night she comes to make their beds,by pulling up the twigs with her beak.By doing that it creates air pockets.So when the chicks sleep at night (colder)on that area their body heat will keep warm air underneath them.
Funny that they are still trying to sleep underneath her, as when they did when smaller.When really young they have no control over their body heat(can't regulate it) so their parents slept on top of them to keep them warm.