What designation should be assigned to a teacher's trainer who is also teaching in the same school? I  joined as a teacher's trainer in school for a short cntractual period. But gradually I started getting involved in the following:   

1- Helping teachers in developing lesson plans

2- Providing feedback to teachers ( I sit in the classroom when they teach) 

3- Motivating teachers ( and principal)  and students 

4- Assist in developing teaching aids

5- Teaching science  ( class 6 and 7 students)

6- Guiding students on Science, Robotics, and AI projects, helping them innovate and think creatively. ( I am an engineer by qualification and a teacher by passion) 

7- Assist in Curriculum and syllabus development along with textbooks selection 

8- Help in the Assessment of kids. 

9- Advice the higher management including the chairman regarding the development and improvement of the school.

10- Career counseling   

11- I am trying to improve teaching and learning experience and taking many creative and innovative steps in the school. Fortunately, I have the authority to introduce new methods and processes. 

My contract has been revised and it seems I will stay here for another 2-3 years. 

I report only to the director and chairman. We have to define a designation for this job. What could be the most appropriate designation title for someone who is working on the above 11 fronts?   

I am basically responsible for overall school development as per the vision of the school including academic improvement (especially better levels in Science and maths).
You seem to have multiple roles. For teaching responsibilities with respect to students you are "instructor" or whatever other designation your institution uses for that. 

But part of your duties are "Instructional Designer" or maybe "Curriculum Designer".

And the third role is "mentor" to the instructional staff or another term with the same intent. In my world, the word "shepherd" would apply, but some would find it odd, perhaps. "Supervisor" only applies if you have some power other than giving advice and counsel. 

But an overall term might just be "Curriculum Consultant" or similar.