It sounds like you have the majority of the parenting time with your sons. If you have an existing order, the courts will be hesitant to give your ex less parenting time without a really good reason to do so. It is likely your best option to negotiate a re-allocation of the already ordered time.
For example, you could trade one school day a month with your ex in exchange for one week of parenting time at spring break. This type of negotiation can be done between the parties directly, with the support of a parenting coordinator or mediator, or with the support of lawyers.
Any guidance provided is not covered by solicitor–client privilege, nor is it taking into consideration all of the facts of your matter beyond those in the question. The legal information is specific to British Columbia Law. If you want a more thorough and case-specific analysis of your legal matter, please contact us to arrange a consultation.