My elder 2 are 19/16. We have just been on a week long music course . THey are both well post grade8/diploma standard recorder players.
They played a trio sonata in the concert (a duet with harpsichord and and a bass instrument if you don't know) and it was amazing 
They only had 4x 90min sessions to prepare it in, and it's the first time they've really played together (it's taken them a while to mature into the realization that they are both equally competent, and can take direction from each other if needed) .
The eye contact and electric communication was stunning. THey just knew how each other was going to deal with a phrase. THe sibling link was clear.
(and no, not at music school, nor doing music at undergrad level either! )