No. Section 19 Permits can only be used by the organisation named on them. If you are lending your minibuses to another organisation, they will need their own Section 19 Permit or PSV Operator’s Licence. It is your responsibility as the vehicle owner to ensure they have the right permits and their drivers have the right licences.
If you are borrowing a minibus from another organisation, you will need to display your Section 19 Permit in the front windscreen. Which is why it is advisable to apply for spares.