1. No a third party can not file an appeal, he does not have a locus to file an appeal.
2. You can file an impleadment application and can be a part in the appeal. Bear in mind that there happens to be no specific procedural so, so a lot depends on the discrition of the commissioner.
3. As told earlier there happens to be no specific procedure, so a lot depends on the discrition of the commissioner.
Regards