First, the practicalities, only the person who originally imposed the covenant and the other owners of properties in the area could apply to Court for an order that the covenant is enforced against you.
A covenant of this nature is usually imposed by developers who wish to secure the residential continuity of the development to protect the property and other from a diminution in value because of environmental factors resulting from a business trading there.
I suppose that in a (very) strict interpretation of the construction of the words the act could arguably be said to be a breach, but not on a broad interpretation and it's certainly not in the general spirit of the covenant (which a Court would be mindful of - it is intended to prevent someone opening a shop with all the noise and disturbance that follows with it. A company renting in the course of it's business to residential occupiers would not cause any greater disturbance than if your brother were occupying it as it's home. It would be a pretty unsympathetic Court to impose it in my view.
In any event your brother can a obtain restrictive covenant indemnity policy to cover the cost of any loss suffered as a result of enforcement action being taken (and for the legal costs of enforcing this). If you google this you will see plenty of insurers will to provide such a policy.
Your brother should also speak to his conveyancer to take his view on the covenant, presumably your brother told them of his plans for the property but I should be extremely surprised if his view departs very far from mine.
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