Father, Stepmother, mother

It depends on who has legal custody.  You mentioned physical custody, but you did not specify whether legal custody is with one parent or shared.  Since it sounds like the physical custody is shared, it would make sense that legal custody is also joint.  But I have seen some rare cases where one party has physical custody and the other party has legal custody.  Assuming you have joint legal custody then the parties must confer about any major medical decisions and make a joint decision.  If the parties cannot reach an agreement, the issue can be taken in front of a judge to decide. This answer is given in accordance with the laws of Virginia and may not be applicable in any other state.  It should not be construed as legal advice, as that would require a more thorough analysis of all of the facts involved in a specific case.  If you need further information or assistance, please feel free to contact my office for a consultation. Case results depend upon a variety of factors unique to each case. Case results do not guarantee or predict a similar result in any future case.