You can file a police complaint (criminal case) for nuisance, or file a suit (civil) for nuisance. 

In criminal case, you need not take consent of neighbours. You will be the complainant and then it's the police responsibility to investigate your complaint and prosecute the offender. 

If the police seem lethargic in recording your complaint, you can file a private criminal complaint before the magistrate having jurisdiction. He will carry out an inquiry and if primafacie if any merit is found in your complaint, he will direct police authorities to investigate and prosecute

If this has the effect of causing public nuisance, report this to the Police. 

If the level of noise being generated by them is more than the permissible limits, this is a fit case to be reported to the Police. 

Not necessary that all the flat owners should sign the Police complaint. You may alone take up this fight.

file police complaint against your neighbour as noise decibel level exceeds 55 DB 

2)if police refuse to lodge complaint file private complaint before magistrate under section 156(3) cr pc to direct police to investigate and submit report 

advisable that other flat owners should join in filing police complaint 

You can give written complaint to the police against your neighbours for public nuisance, if the sound exceeds the permissible limits.

Section 268 the Indian penal code which defines public nuisance is reproduced as follows for your understanding:

268. Public nuisance.—A person is guilty of a public nuisance who does any act or is guilty of an illegal omission which causes any common injury, danger or annoyance to the public or to the people in general who dwell or occupy property in the vicinity, or which must necessarily cause injury, obstruction, danger or annoyance to persons who may have occasion to use any public right. A common nuisance is not excused on the ground that it causes some convenience or advantage.

Yes definitely. If you choose the criminal case option, the offender will be punished. If you choose the civil suit option, civil judge will pass a decree ordering him to stop the nuisance and you will he compensated in monetary terms for the nuisance you suffered till Now. The wrong doer will be decreed to compensate you

You alone can file a complaint against the neighbour but it would be better if the complaint is signed by others as well.

You can complaint before the police for nusicance cause by the neighbour if the hours of such bhajan are not proper the police shall take step.

You can also complaint before the state pollution control board 

It is sufficient if you alone sign such complaint though it would be good if other flat owners joints proceeds agaisnt the person 

See that would be based on facts and circumstances you can still move ahead 

you should get solution to your problems 

It is better to issue a legal notice to the other party demanding to keep the noise level within reasonable and permissible limit and claim  for compensation for disturbance caused to you. 

In default file a suit for injunction restraining the defendant to cause nuisance by making high sound. 

You can file an injunction suit in a civil court for restraining such nuisance. If there is any damage that has been caused to you earlier by such act , such damages can also be claimed by you in the civil court.

File a police complaint followed by injunction. 

You can yourself file a complaint. You need to file a suit and take injunction for the same

This bajans happen only once a month hence this cannot be treated as a continuous nuisance as well.

However you can lodge a complaint with the local police on this nuisance .

They will take action by first giving them a warning and then proper legal action.

If the other flat owners are also affected by this nuisance they may also join you in signing this complaint or you alone can also give this complaint.

Dont approach to this problem with a negative thought, you confidently approach police for proper action as per law, let them do their job.