The head of company alternates between someone who has been brought up by our company the start and someone who has been brought from our mother company
The head of companyは our CEOや our CFOに置き換えてください。
生え抜き社員は直訳されるとelite workerとされていますがこのsomeone that has been brought up by our companyは最初から会社に育てられた社員なのでこちらの方がいいと思います。
親会社はmother companyです
オーストラリア 
