1 - The presence of the chairman of the board coupled with his two sons means that a very important decision will be made. I am expecting that one of them will inherit the responsibility. [responsability of what?]
2 - Your brother has made a lot of wrong decisions, which caused the failure of his marriage. In the same way, I can see you following his steps. Pay attention to your actions before you regret it.
3 - I don't care all that much about my clothes style. I think simple and colorful clothes are enough for me. On the other hand, my brother cares so much about following the latest fashion trends; my cousing also has his fashion sense [a better way of writing it]. They always spend a lot of time shopping together.
4 - Three things that you should follow to be a good teacher; first, be respectable. Respect your students, and don't accept anything from them other than respect. Second, be funny. Who likes a boring teacher?! try to make a funny atmosphere to keep your students attention always. Next [we don't normally use 'third'], be concerned. Never ignore any of your students when he tries to talk to you even if it's about personal matters; always listen.
5 - In the light of the latest events in our school, there must be a deterring punishment to anyone who contravenes the schools rules and instructions.
Your sentences are pretty advanced - I had fogotten what 'contravenes' meant, and I'm a native speaker! - sometimes they are awkward though.
1. 7/10
2. 8/10
3. 7/10
4. 7/10
5. 8/10
