Yes, your lecturers/professors have access to your academic records, including your past grades.
This may vary depending on the institution and their policies. Generally, lecturers/professors have access to your grades from the time you enrolled in the program.
Yes, as long as the grades are on your academic record, your lecturers/professors can see them regardless of the course or program.
Most institutions have policies in place regarding the privacy of student records. You can inquire with your academic advisor or the institution's registrar to see if there are any options available.
It is the responsibility of lecturers/professors to assess your current performance and not base it solely on your past grades. However, it is always best to work hard and improve your academic record to showcase your potential.