[Ichthypresbyter]

AIUI a Catholic monk who is also an ordained priest is addressed as Father not Brother (certainly this is true of the Dominicans I've met).

I think this is also true for Orthodox monks.

I'm not sure if there's a Christian denomination that has pastors who aren't priests, and also has monks. So this sounds to me more like a situation where all fellow members of the church are addressed as Brother/Sister.