You can do this, but you will need to expend multiple uses of Channel Divinity.
Channel Divinity: Destructive Wrath (PHB, P. 62; emphases mine)
When you roll lightning or thunder damage, you can use your Channel Divinity to deal maximum damage, instead of rolling.
Note that this use of Channel Divinity is for a damage roll, not for a spell. It can be for any effect that causes lightning or thunder damage.
If you expend a sorcery point to Twin Spell a Witch Bolt, you will have two spell attacks that could each do damage. Each is a separate damage roll, so each would require a separate use of Channel Divinity to maximize. The ongoing damage each round from Witch Bolt is another separate roll, and thus would require another use of Channel Divinity. Given that clerics have a maximum of three uses of Channel Divinity between rests (and that at 18th level), this is probably not that efficient.