Is it "OK" for relatives to work at the same company? Why yes or not?

SAme company is ok, same department or section is not OK.

Because its not ethical to employ your relatives which is seen as a sign of favoritism. Below brief explanation on the same:

The employment of relatives in the same area of an organization may cause serious conflicts and problems with favoritism and employee morale. In addition to claims of partiality in treatment at work, personal conflicts from outside the work environment can be carried into day-to-day working relationships.

“For the purposes of this policy, a relative is any person who is related by blood or marriage, or whose relationship with the employee is similar to that of persons who are related by blood or marriage.

“Relatives of persons currently employed by XYZ may be hired only if they will not be working directly for or supervising a relative. XYZ employees cannot be transferred into such a reporting relationship.

“If the relative relationship is established after employment, the individuals concerned will decide who is to be transferred. If that decision is not made within 30 calendar days, management will decide.

“In other cases where a conflict or the potential for conflict arises, even if there is no supervisory relationship involved, the parties may be separated by reassignment or terminated from employment.”