1) write a handwriten clear concise and objective letter to the police/coloner + a letter to the family. Put your reasons and state that its not your family fault and there is nothing that could be done to change your decision. Also make it clear that CTB is your own responsabilty and nobody else assisted you and you are in peace with that decicion to CTB.
A letter to the police could somehow help (there is controversy) but you want the investigation to be concluded asap and smoothly after you CTB. No one whants big police interrogatory to your family members, so make your CTB something clear and with all evidences exposed.
Find bellow the best tutorial of how to write an effective and objective Suicide letter to family:
HOW TO WRITE A SUICIDE NOTE