Scottish deed of assignation

Help with Scottish trust law please

Settlor Mrs A completed the mentioned deed assigning a policy to trustees.
The trustees being Mrs A, Mr A and Corporate trustee.
It is signed by Corporate trustee but the signature for Mrs A is signed by Mr A (as attorney for Mrs A)

Can Mr A do so or should he sign in his own capacity as trustee?
Should there be a power of attorney document in place for this?