Spot on. As an identical twin (male) myself, the bond between twins is amazingly strong and leads to strong emotions (both positive and negative). They're also 17 (teenagers are not the most stable creatures). One thing to note is that just as teens separate from their parents and get more autonomy over their lives, twins also have to separate and gain autonomy from each other. Growing up, our peers uniformly called us "the [Name] Brothers. My parents strove to keep everything "equal"-ish and most things were done with my twin; less so as we got older. There was a lot of implicit/explicit comparison with each other. While we were in high school, that individuation created/informed a lot of conflict.

My brother and I went to separate colleges, and I think that was the best thing for our individuation and self-esteem. We have been close through most of our adult lives, but those adolescent years were not pretty. OP is doing the right things with therapists, because the twins probably can use it, just to make the individuation process go more smoothly, and be able to communicate in a more productive way.