Hello shaileshji,
Well technically rental thing seems okay, but practically when if at all it comes to representing the facts with department, complete details has to be given such an arrangement shall be caught and disallowed because:
-since the assessee has a flat of his own in the same building there is no requirement to take flat on rent and that too from his relative only.
-secondly though this arrangement seems to be profitable and successful one, the major drawbacks are:
1)flat in same building
2) flat of his own brother.
due to these two reasons, the assessee is at risk coz ultimately at the department, all the details are required to be submitted especially the address of his own flat and his rental flat.