Chargesheet basis concrete evidence ?

only the verbal allegation is enough for filling the chargesheet by the IO for arresting the accused ?

Yes.. but arresting vary from place to place. in our case till now no arrest chargesheet submitted 4 months back.

If concrete evidences is not available then chargesheet can be filled or not ?

Yes

is there any situation in which IO is not able to file chargesheet and case was rejected by the court ? on the same basis ?

IO has to submit his chargesheet to court then only court proceeding starts

answer are on personal experinece.. i am not a lawyer

Fighting for my brother has gained a good legal knowledge despite not bin an advocate, well the exposure and experience would have helped her to achieve them.  About the query, she is right, the court will proceed with the case n the basis of the charge sheet.