I believe your problems stem from bringing Ollie in. If there was peace in the household before and after he was brought in there wasn't that is almost certainly the issue.
When you brought him in did you do a proper introduction? As in, keeping them separated from a week or more, getting them accustomed to each other's smells by exchanging sleeping blankets, exchanging rooms after a week or more, etc.
If you just threw him into the mix expecting the kitties to find their own place it doesn't work that way. I have found that out through trial and error myself.
Ollie being used to fend for himself outside had learned how to fight and fight well. Gracie watched Ollie dominating Charlie and now figures it's ok to do it herself.
And, as L4 mentioned, it would be a good idea to take Charlie in for a full checkup to rule out him being sick. Sometimes if a cat is sick other cats can sense it and react by attacking the weaker cat. It would not be a bad idea to take Gracie as well as she could be under the weather herself and protecting herself by being aggressive. Is she spayed? If not why not make the appt to get her spayed too. Her hormones could be all over the map going through heats, etc.
My suggestion is to do a reintroduction and see if that helps. Separate them completely for as long as it takes. No seeing each other at all. Give Charlie a safe room where he does not have to worry about being bombarded by Gracie. If he has a litter box, his food and water, a bed and a window to look out of he will do just fine.
This is my favourite site for instructions on how to introduce cats. This lady didn't just write an article. She walks the walk.
Just for my nosiness......... you mentioned "wet food day". Does that mean they only get wet food one day a week? Not that is has a lot of bearing on the fighting (although if Charlie is indeed not well it could have in a roundabout way) but a good quality canned food is tons healthier for them than dry food. Cats are meat eaters. They do not do well on a diet of corn and grains which is what dry food is. Humans can't digest corn. I don't know why the pet food companies feel cats can.
A great site for doing some research into that issue is:
Good quality foods are any that are corn and grain free. Also with no by products. Wellness, Natures' Variety, Evo, Natural Balance are just some of the great wet foods you can look for.