Hey Ryan,
You have tried to sort this out biblically by going to him personally. Now bring in a mutal friend/leader and talk with him together. If that doesn't work, take them to the Church leadership.
Either his leader/pastor asked him to take responsibility for these areas or he doesn't like how something is being run so he has decided to do something about it.
If it's the first, try and find out why. How did you and your father come to be in the role? If you were asked by a church leader, I would seek their counsel as they may have insight into the background of the move. It may be that Church leadership are seeking to streamline processes and therefore put one person in charge of those 4 areas (that work closely together). This is true of growing churches where having the numerous teams accountable directly to the pastor isn't practical.
If it's the second, he needs to be correct – not by you but by his superiors. I would speak with his boss/pastor and explain the situation. Try your best to leave personal attacks out of it. It's hard not be be offended when you see someone tearing down what you have established. This isn't about you, rather the safety and security of the church so go with the heart to better the systems regardless of who you need to work with.
Although his execution of leadership leaves something to be desired, if Church leadership have put him there you need to try and work with him as best you can. Submission creates a way for favour. Walking in love will earn people's respect. This Christian walk isn't an easy one :D