I also haved a three peoplerson interview with my homeroom teacher, my mother and meyself. I also had a three person interview with my homeroom teacher, my mother and myself.

use past tense, it has already happened. when describing something we say person, for example a "five person car". You are the subject and object of this sentence so use myself.

I also have three people to interview withincluding my homeroom teacher, my mother and meyself. I also have three people to interview including my homeroom teacher, my mother and myself.

I also have three peoplean interview with my homeroom teacher, my mother and me. I also have an interview with my homeroom teacher, my mother and me.

I also have a three peoplerson interview with my homeroom teacher, my mother and me. I also have a three person interview with my homeroom teacher, my mother and me.

"N person X" is the way of saying an "X" that requires "N" people. I agree it would be more logical if we used "people" here, but that's not how native speakers phrase it.

This is howBecause of this I couldn’t study for a few hours so I will definitely study 12 hours tomorrow. Because of this I couldn’t study for a few hours so I will definitely study 12 hours tomorrow.

if it is happening tomorrow it is in the future, so use future tense.

This is howwhy I couldn’t only study for a few hours, so I will definitely study 12 hours tomorrow. This is why I could only study for a few hours, so I will definitely study 12 hours tomorrow.

This is howwhy I couldn’t study a few hours so Ifor a bit so I will definitely study 12 hours tomorrow. This is why I couldn’t study for a bit so I will definitely study 12 hours tomorrow.

This is howwhy I couldn’t study a few hours so I will definitely study 12 hours tomorrow. This is why I couldn’t study a few hours so I will definitely study 12 hours tomorrow.

I went to school to practice for the sports festival’s dance today also. I went to school to practice for the sports festival’s dance today.

No need for also, you only said one thing.

Today, I went to school to practicse for the sports festival’s dance today also. Today, I went to school to practise for the sports festival’s dance.

I went to school to practice the dance for the sports festival’s dance today also. I went to school to practice the dance for the sports festival today.

I went to school to practice the dance for the sports festival’s dance today also. I went to school to practice the dance for the sports festival today also.

It's grammatically ok to write "the sports festival's dance" but you need the "the". However, I think in this case it's more natural to say "the dance for the sports festival"