a) Service fees charged by HC to your subsidiaries should be on an arm-length basis. Otherwise, tax authorities will have the right to adjust the price.
b) Contracts should be entered to detail the service scope and fees. All fees charge by your HC should be subject to BT.
c) If HC signs contracts with other enterprises on behalf of their subsidiaries, or pays the service fees on behalf of their subsidiaries, and later gets back from their subsidiaries, this kind of revenue is free from BT.