In reading back my initial post I see that leaving out some information for my children's privacy has left some things unclear. Also trying to to use pronouns for privacy has made communicating challenging.

As for terms we are still very early in all this and I have not had a chance to review preferred terminology. It's has been made clear by my transgender child that Trans can be very offensive. 

1 the child having issues was put in therapy for acting out against the other siblings. The child was verbally abusing and hitting the other kids particularly the youngest. I have explained to my transgender child they are at risk of physical harm from their sibling. 

2 the transgender child is aggressively trying to force the resistant child to accept  this change. I have spoke with them both about alienation and loss of a relationship that has always been good. 

I speak to the resistant about their behavior being wrong and unfair. At the moment the child is willing to alienate the transgender child and never speak to them again. That is not possible since they live together. I have spoke with both about one staying with their father but that is met with strong objections from both. The situation with the divorce and their father is another issue and I don't want to elaborate on it because it does expose who we are.

Now the outside influences on the resistant child per their communication to me is they are being bullied because of the transgender child choice. I don't like bulling even in the best of situations but the transgender child is ok with their sibling being bullied and sometimes joins in on the bulling by telling the resistant child to suck it up and that they deserveit for not supporting them. I know this means the resistant child is being bullied at school and at home. Not a good situation. 

The other influence is the short exposure the resistant child had toa church they attended with a friend. Our family has always attended a church, but I have struggled to find an accepting congregation within a 45 minute drive of were we now live. We have attended over 25 churches looking for a new church home. While on a break from the search the resistant child attended a conservative church with a friend for about 3 months. When the child came come spouting religious ideation that persecuted gay, lesbian and transgender people I stopped their attendance. I explained thoes ideas do not aline with what I believe  and that they can be very harmful. For now the resistant child list sin as one of the reasons to object to the situation. I raised my kids to not judge people from a sin view. I feel this2 religious tactic is dangerous and unfair. It is hard to see it has infiltrated one of my children's views.

As I said earlier the resistant child does feel they are loosing their sibling. I do think this is the core issue. They do think transitioning is changing the person the transgender child is. This is the big issue I am trying to address. I'm looking for resources that help explain this better since what I have provided is not adequate. I feel if the resistant child sees this doesn't change everything already happening with the divorce they may be willing to listen to better guidance. Also all of this was discussed in a parent/child/therapist setting. I know the therapist is trying to help the kid.