A teaching permit can have two teachers and/or two students. It requires that the teacher(s) and student(s) are close relatives (parent, guardian, grandparent, child, grandchild, sibling). If the teaching permit is granted to two people, one of them must be designated as the responsible teacher. If these conditions are not met, the new teacher must apply for a permit separately.
More information about the teaching permit can be found here: https://traficom.fi/fi/liikenne/autoilijat/ajokortit/hae-opetuslupaa