You will need to remove the dash to get to the duct work just to clean it properly. You may have some damaged blend doors that will need to be replaced. If you need further help, reach me via phone at https://www.6ya.com/expert/steven_a67ead41eb5fc62a
First, you have to find the leak. It could be a freeze plug or a hose. Properly mixed coolant (antifreeze and water) will not freeze. If you can't get the car inside, you'll have to wait until the weather warms up above freezing to look for the leak.