You should definitely tell any coaches recruiting you as soon as possible. That is the right thing to do. The sooner you do it the sooner they can adjust their recruiting strategy elsewhere. How to do it depends on the relationship and the recruit can be the judge of what is appropriate. If I have a personal phone relationship with a recruit and have developed a good relationship I would expect a phone call. If my relationship has been mostly email-based and we haven’t spent a lot of time chatting an email would be fine.
Most coaches will congratulate you and wish you well. That’s what they should do, in my opinion. If they don’t and they try to make you doubt your decision, well, you just learned something more about that coach. For me or my child that would not be a positive thing to learn and would only confirm the decision.
After a recruit makes a decision on where he is going to go is it a good idea to inform the other coaches that are recruiting him? Is the best way to do that by, phone email or how would you recommend going about doing that/