“Section 9 does not automatically lead to the court reducing the child support payable by the higher earning parent by the amount of support owing by the lower earning parent. The courts have found that the simple set-off approach is the preferable starting point, but it must be followed by an examination of all the factors, including assessing whether the support-receiving parent will be able to continue to meet the needs of the child. The court tries to avoid a significant variance in the standard of living between households for the child of the relationship. Contino v. Leonelli-Contino, 2005 SCC 63.”