Classes have also started at music school now. I go twice a week for piano. I'm continuing my tennis lessons. Oh yes, I've been moved up to the "older" group in tennis.

Wednesdays I go to Auntie Mike's for English lessons.
Tuesdays I have choir practice. Those are my responsibilities.
I have six lessons every day except Fridays. I'll survive...

(Are they grammatical? Would you check them?)

All of your sentences are excellent.

Yes, I can check the sentences for you! Let's go through them one by one:

1. "Classes have also started at music school now."
This sentence is grammatically correct. It states that classes have begun at music school.

2. "I go twice a week for piano."
This sentence is grammatically correct. It mentions that the person attends piano classes twice a week.

3. "I'm continuing my tennis lessons."
This sentence is grammatically correct. It indicates that the person is continuing with their tennis lessons.

4. "Oh yes, I've been moved up to the 'older' group in tennis."
This sentence is grammatically correct. It reveals that the person has been promoted to the "older" group in their tennis lessons.

5. "Wednesdays I go to Auntie Mike's for English lessons."
This sentence is grammatically correct. It explains that on Wednesdays, the person attends English lessons at Auntie Mike's.

6. "Tuesdays I have choir practice."
This sentence is grammatically correct. It states that the person has choir practice on Tuesdays.

7. "Those are my responsibilities."
This sentence is grammatically correct. It establishes that the activities mentioned earlier are the person's responsibilities.

8. "I have six lessons every day except Fridays."
This sentence is grammatically correct. It mentions that the person has six lessons every day except for Fridays.

Overall, the sentences are grammatically accurate!