Hello and welcome *hugs*
Well its up to you what you say since you know them best... you might talk about it with a gender therapist first...
you might look up a brochure called "doh-transgender-experiences.pdf" . Only thing I would disagree with is page 7, where they state stress, instead many experience relief.
It states that being trans has biological connections, to do with development before birth which influences the sense of self.
So its not a light hearted decision, and there are many feeling this way. Its nobodys fault, neither theirs nor that of their upbringing.
And it explains some of the feelings transgender people have.
You might think about showing the brochure.
You additionally might give an explanation of a twin... they will be essentially the same person... like a female twin... with still the same sense of humour etc...
And you might look up the genderbread person.
It shows that gender identity, gender expression, etc are different things.
Its possible to click on the picture to see it larger.
And, well, concerning talking in general it might help remain calm and relaxed, stating facts and needs, without getting upset or angry.
"Am very accepting of my MTF child (16yrs old). Want to help him get on hormone therapy, but not sure where to look. The endocrinologist my husband uses doesn't do therapies but our marriage counsellor does do trans therapies. Should I ask her or look out side my area (Chattanooga, TN). My husband still thinks this is a phase and will pass (but is quick to point out he had gay friends)."
Well if the counselor also does therapies for transgender people it might be a good choice...
you might ask her to keep it confidential...
You might ask how she sees her role... she should help through the process, not gatekeeping... and how long it would take with her until getting hormones...
she should know an endo or doctor who would prescribe hormones...
for support you might ask at the next lgbt center near you, at plannedparenthood or at pflag...
and you might simply ask the therapist, they might know support groups, too...
hugs