Can a project manager client side work as project manager Contractor side?

If there is a conflict between two associated companies and the project is realisation is posponed or cancelled what will be the compensation for the project manager from those companies?

Depends on the Project size and the number of Vendors involved.

Scenario 1: If the project is very small and has 1 vendor then Clinet PM can be the Vendor PM and vise versa, however an acceptance test of delivery needs to be performed by the client team 

Scenario 2: If the Project is big and involves more than 2 vendors. Theoretically yes, but better if avoided, reasons being :

1. Conflict of Interest 

2. Vendor might be might be executing a small part of it. So the project manager from the client side has to have a bird's eye view to check the interdependencies.

2) Risk of compromising on quality

An other option could be to make the vendor accountable for managing the project and other vendors associated rather than directly managing them, but you would still need a person who will manage the vendor doing project management 

I wouldn't suggest it mainly because of Conflict of Interest. Other reasons being,

1) The project might be a big one from the client's perspective and the contractor might be executing a small part of it. So the project manager from the client side has to have a bird's eye view to check the interdependencies.

2) From the quality perspective it's better to verify the delivery from the contractor from the client's perspective which one can lose if working on both side.

Hope this answers your question.