Hello Experts
My father had construction material and he is staying in city ‘thane’ and the material was dispatched to a supplier “A” at Mumbai & an agreement was done. My father was given monthly rent on those materials for a few months but later supplier cheated and we stopped receiving rent. On repetitive chase, we came to know that supplier had further rented material to a 3rd party who had ditched on the payments to the supplier.
The agreement between my father and supplier “A” had two conditions as follows:
1. the material will not be transferred to any third party
2. all disputes for money & material will be settled through arbitration.
This supplier has cheated us, there is a breach of contract too. Equally the supplier has filed a private suit against the 3rd party for recovery of his money where my father is not a party.
Please assist me with below 2 points:
1. Can my father add himself as an obstructionist or as a new party in the suit between supplier & 3rd party as his material was secretly given to 3rd party. This suit is at Mumbai
2. Can my father file arbitration proceeding at Thane (reference section 20 CPC which states part of cause of action at Thane as material is supplied from Thane & my father stays at thane)..All other legal formalities of earlier agreement were done at Mumbai.
Please advise 
