ANSWER
Each sibling will weed 2 1/4 square yards of the flower bed
EXPLANATION
The flower bed is 9 square yards. 4 people - Matthew and his 3 siblings - weed equal parts of the bed, so we have to divide the flower bed in 4:
We can divide the first 8 square yards in 4 groups of 2 yards, but the last one we have to divide it in 4, so 1/4 for each sibling. Therefore, each sibling - including Matthew - will have to weed 2 1/4 yard of the flower bed.
