That is the hard and dangerous way to trim hooves.
You should be able to find some "foot rot sheers" in the hardware store.
Handles similar to the proof photo of the secateurs, but with straight blades, like scissors on steroids.
If you leave it too long between trims the smell will tell you why it is called "foot rot".
The feet do actually rot away/get eaten away and the sheep can hardly walk
I'll look into that, and we will keep an eye and nose out for the foot rot.
Have a look at some of the NZ shearing competitions, they may give you an idea on how to sit the sheep so it stays still while you work on it.
about $NZ 18
about $NZ350 [cordless]
Is there enough sheep in the neighbourhood for a pro shearer? or, do you intend to hand shear them or acquire a small shearing plant?
If you do it by hand, your hand will be so strong that nobody will shake hands with you afterwards:)