Sure, it's possible provided his parents are able to pay around $15,000 in tuition per year. He will need to be accepted by a school and then apply for a study permit.
Tuition fee is a non-issue, can you tell me the process or guide to where I can find how to get admission?
You will need to contact the school he plans to attend to determine if they are willing to accept a international student. Then he'll need to apply for a study permit: https://www.canada.ca/en/immigration-refugees-citizenship/services/study-canada/study-permit.html
I know how to apply for a study permit since I am currently waiting on my application. How do we look for admission in schools for A-level studies, is my question.
Someone will need to spend time contacting schools in the area where your siblings live to determine if any of them are able to accept international students at this time.
As @scylla said, you can get accepted into school but it will be hard to find a school that provides A-Levels in their curriculum
