Is a tenant bound by the fixed term of an AST if the property is sold

Tenancy Types and Management

I have some prospective tenants who would like to enter into a tenancy agreement for one of my properties. However here's the problem:

1. They previously rented property A from landlord A
2. Due to problems with Landlord A they gave required notice to terminate the tenancy of property A
3. They signed a new tenancy agreement for property B with landlord B, this tenancy has a 12 month fixed term
4. They have now been informed that property B, is being/ has been, sold to Landlord A. Clearly they are unhappy with this situation as they previously had problems with Landlord A and were only moving to get away from them.
5. They have now viewed my property and would like to go ahead with entering into a tenancy agreement for it rather than moving into property B.
6. They have been informed by Landlord A that they are committed to stay in property B for the 12 month fixed term.

As I understand it point 6 is actually correct. However It seems unreasonable that when a landlord is considering purchasing a property with in situ tenants he can vet those tenants and does not have to go ahead with the purchase if he is unhappy with them. However the tenants have no choice but to accept whatever landlord they end up with as a result of the sale and are stuck with him/her the duration of the fixed term.

So my questions are is point 6 correct or do tenants have the option to leave? Is there any other way prospective tents can avoid having Landlord A and rent my property?