It is not possible, since we only work with the most affordable rates and they do not give the option of adding animals.

You can do it directly through the train company.  Some allow dogs, cats and other small animals (maximum two per passenger) provided they do not endanger or inconvenience passengers or staff.  There maybe a surcharge.

• Dogs must be kept on a lead at all times unless kept in a cage.
• Dogs without leads, cats, birds and small animals must be carried in an enclosed cage or pet carrier
• Animals and containers must not occupy seats, othewise a charge will be made.