Did you see this note when you want to share a group?
"Sharing a group with another teacher is simple! First, be sure all students in group are shared with the teacher first before sharing the group. Once shared, '2 Vocab and Comp' will automatically appear in the teacher's group list."
The '2 Vocab and Comp' is the name of one of my groups. Would this work for you to share the individual students first and then add the teachers' names on the groups?