Is it possible at this stage that all sindhi punjabi & Bengali Hindus unite on a common platform and seek justice?
What you suggest is the most desirable step to take but taking up the case with international bodies or seeking justice costs a lot of money and motivation. Hindus do not have either for a good cause.
Most of us are resigned to fate and regard it Will of Bhagwan that we were exterminated in Pakistan! Moreover most Hindus regard traitor Nehru and "goat" Gandhi far above Bharat Mata on the scale of reverence, and so they cannot question their (Nehru's and Gandhi's) patriotism even in dream! Ignorant, gullible and foolish Hindus choose leaders who hate them and wish them to perish, e.g., NEHRU who made NO secret of the fact that he cares two hoots for Hindus or their temples!
Had autocrat NEHRU been a devout Hindu like Shivaji the Temple in Ayodhya would have been reconstructed within days after he took over the "broken, bleeding" Bharat in 1947. Where there is Will, there is the Way! Please recall the SPIRIT of the Sikh community. Within days of malicious, arrogant and autocratic attack on Harmandir Sahib that reduced Sri Akal Takht Sabib to smouldering smoking ruin, the Sikhs rallied fearlessly and reconstructed the destroyed building within days. Why didn't the Hindu nation feel similarly committed and inspired to rebuild the Sri Ram Temple in Ayodhya within days?
Such a nation that does not care for the greatest and the holiest national temple in Ayodhya, is not expected to ensure justice for the Hindu refugees and destitute of 1947. On the other hand we see the Muslim countries promptly finance their cases at the highest level and obtain favourable decisions by Courts. If even one tiny mosque is destroyed in Bharat the entire world will be in uproar, but who cares for the HUNDREDS of temples that were destroyed and left to become ruins in Pakistan?
It may be another century when the Hindus become stalwarts. Today we are a demoralised and fearful lot if LOK SABHA has not even discussed a Memorial to the TWO MILLION dead of 1947.