Claim Form for possession of property (Form N5)

Possession - Section 8 and Section 21

Good afternoon. I'm in the process of completing a claim for possesion of a rented property.
The claim is based on rent arrears and breach of various clauses in the agreement.

The most recent agreement only makes mention of one of the tenants although the original agreement mentioned all those that are living in the property.
When completing form N5 should I name each tenant as defendant or should I only use the name of the person who is on the latest agreement?

Also, is there a specfic formula used when calculating rent arrears?
Can I use a basic spreadsheet and show the monthly difference between the rent and the amount actaully paid?

Many thanks for your time.

Jacqueline Glaze