Whether professional misconduct?

If the derctors Brother Has been (in the past ) a partner there in no legal barrier under company law

Howerver pronouncment of the Institute on "Independece of an auditor " states that a PCA  shall take attmost care to be in indepndedt state of mind while conducting any audit assinment

so the PCA shall take care of that asspect

but as no dirct relation can be established it can not be termed as a missconduct...