I don't know how they will help them feed the chicks for the next month which is apparently how long they will need to. From what I've managed to dig up on the web, eurasian kestrels stay in the box for at least 5 weeks and then with parents for another month or so until they learn to hunt.
A nest of 5 would require the parents to hunt approximately 7 times a day so as TPC said there is no way Rebecca could manage that all on her own. I'm just worried that in her quest to try and feed her babies, she will forfeit her own life. I know..it's nature..
Couldn't find much on behaviours of parents. They do mate for life but in the event of death they will take on a new mate but no details on whether that would happen in an event where the female/male already has a brood. They have an extremely high mortality rate as well, 70% don't make it to live 2 years.