Could you please tell me if the following sentences are possible? Thank you.

The principal of my school has asked me to find an Irish school which
would be interested in a Comenius partnership with our school, a French high school and a German high school. 2) The project will be mainly about a comparative study on biodiversity in water and other waterways in our local areas and English has been chosen as our lingua franca.
3) Our preliminary meeting will be held on 27. January and 28. January.
It would be extremely important if your school could join our partnership.
4) Hoping that your school is interested in a partnership with our
school, I send you my best regards from Italy.

All are correct.

Yes, all the sentences provided are grammatically correct and possible.

To confirm this, each sentence is examined individually:

1) The principal of my school has asked me to find an Irish school which would be interested in a Comenius partnership with our school, a French high school, and a German high school.

To determine if this sentence is possible, we need to check if the sentence is complete and coherent. The sentence has a subject ("The principal of my school") and a verb ("has asked"). It also has a clear request stated, which is to find an Irish school interested in a Comenius partnership. So, this sentence is grammatically correct.

2) The project will be mainly about a comparative study on biodiversity in water and other waterways in our local areas, and English has been chosen as our lingua franca.

This sentence seems complete and coherent. It states the main topic of the project, which is a comparative study on biodiversity in water and other waterways in their local areas. It also states that English has been chosen as the lingua franca. Thus, this sentence is grammatically correct.

3) Our preliminary meeting will be held on 27th January and 28th January.

This sentence provides clear information about when the preliminary meeting will take place, specifying the dates as 27th January and 28th January. The sentence is structured correctly, and the information is clear, making it a grammatically correct sentence.

4) Hoping that your school is interested in a partnership with our school, I send you my best regards from Italy.

This sentence is grammatically correct. It expresses a hope that the recipient's school is interested in a partnership with their school, followed by a statement of sending best regards from Italy.

In conclusion, all the sentences provided are grammatically correct and coherent.