Concern for swan family

Hello, I am concerned for a swan family who live near me. There are 3 cygnets, 3 weeks old. Their mum was killed a few days ago by a dog (suspected) and their dad has a fishing hook stuck in his beak. The RSPCA are aware and are keeping an eye on him but don't seem to be doing anything. I'm absolutely heartbroken about mum, it's just so awful and sad. I wonder if there's anything I can do to help them. I go down to see them every day and feed them. I'm struggling to find reliable advice on what to feed them. I have been giving them dried mealworms as I'd read that this is very good for them but then I just read something else which said that too much protein is dangerous for them. Any advice? Is there anything else I can do to help them? I'm worried Dad's beak might get infected, he is able to move around freely and is feeding.