Sorry to to read about one of the parents, this happens, whether it is a cat, a bigger bird or other. One parent can raise a brood, I think the older they are the better. Parents have to feed an awful lot in a day, so extra feeding would help. Firstly do not be tempted to go near the nest, apart from the fact that it is an offence, you do not want to spook the parent. The chicks need good nourishment, the parent will bring bugs and beasties but you could throw out some sunflower hearts, or either soaked dried mealworms, you get them in bags, (500g)? soak them in water for a while or live ones, if you can handle them, they can be bought online. Scatter a good distance from the nest, the parent will find them. It may work, it may not, the parent may find it tough to bring up the chicks on its own, it may abandon the nest? Sadly this is nature and we have to take the good with the bad. Hope you get on okay and keep us posted. I will have a google and see what I can find. A word of caution, please change your name from your email address, this is an open site and you could be open to spam and unwanted emails. Go to the top of the page on the right, click the circle, go into profile, halfway down the right you will see, edit profile, click that, you will now be able, to give yourself a new name, save profile. You can add a picture if you want, click the avatar, circle will say change, pick a picture from a photo saved or the internet, save profile.