He had 10 siblings, but since Joe Jackson's affair he technically has a step sibling. Which makes 11, But he has 10 cause I don't count Joe's affair child.
From oldest to youngest:
1. Rebbie Jackson
2. Jackie Jackson
3. Tito Jackson
4. Jermaine Jackson
5. LaToya Jackson
6. Marlon Jackson
7. Brandon Jackson (Marlon’s twin brother who died less than a year of his birth.)
8. Michael Jackson
9. Randy Jackson
10. Janet Jackson
(11'ish?) and Joh’Vonnie Jackson if we’re counting the other child conceived from Joseph’s affair.