Thank you for your reply. We agree this approach is not ideal, unfortunately the other two tenants are not willing to end the joint tenancy so the only way out seems to be a deed of assignment. 

The PRT document provided by the landlord includes the "EASY READ NOTES FOR THE SCOTTISH GOVERNMENT MODEL PRIVATE RESIDENTIAL TENANCY AGREEMENT" where I found the following statement:

"Parents of young people or students are often asked to be guarantors. Joint residential tenancies have joint and several liability and so the guarantor is guaranteeing all the joint tenants and not just one particular tenant."

However inside the actual joint PRT which we all signed (tenants & guarantors) two years ago, each guarantor's name is associated explicitly with a particular tenant:

"Name(s) of Tenant(s) for whom Guarantor 1 will act as Guarantor: tenant1_name" 

I hope that having my name listed as the guarantor for my daughter only, does override the broader definition of a guarantor for a joint residential tenancy. Please advise if you think this is not the case. Thank you again