I would use "discuss." The word "discusses" is only used when the subject is the third person singular form (he, she, or it). For example, "Each teacher seriously discusses the problem of bullying in the school with each student representative." If you look up "discuss" on merriam-webster.com, you will see the following examples:
She discussed the plan with several colleagues.
They held a meeting to discuss the future of the company.
We'll discuss where to meet later.
Have you discussed the matter with your family?
In the first chapter, the author discusses childcare issues.
LangLove, Karen123456's post discussed the present tense, of which there are only 2 examples in your list. I'd say that "each xxxx" takes the singular form of the verb, as you say: "Each teacher seriously discusses the problem...". Re Copyright's question, if we add "...and each student representative..." (ie, two people), in my opinion, it'd then be "discuss".