Hi Everyone
1:
I teach art education, and we use Trello boards per semester where students post their weekly art education tasks. A few past students mistakenly created boards which are now attached to my list of boards. These students are no longer contactable; the only thing is they are the 'owners' of the boards so I cannot delete them. They are taking up the amount of boards available to me.
Is it possible to invite students to use the board without this happening again? Not every student does it, but when they do, its very frustrating.
See screenshot. I only want to keep Gallery 501, to duplicate it each time with another class. 
2: I would like to one day upgrade to standard but as the number of students is unknown and they only use it for five weeks each time, does that cost me more as there is only me who would be permanent.
Thanks for your time.