My brother is firmed with his decision not to send their children in Canada however the wife keeps on pushing him now to send their children for medical tests in the Philippines. He's asking for annulment but the wife doesn't like to go back home and spend money from her own pocket. She wants my brother to shoulder all of possible expenses which probably cost them more or less PHP 280,000 or CAD 6,900. So our family is trying to come-up with a solution to resolve the issue by reporting this matter to the immigration and hopefully they will look after the real marital status of that woman and what she did in Canada ( a certified homewrecker) before granting PR status. If that's the case, she doesn't have an option but to file an annulment first and cooperate with my brother.
As already stated, Canadian immigration doesn't care if she is a "homewrecker". It is COMPLETELY legal for her to be sponsored by her current common-law partner while still married to her ex. She is not required to file for an annulment before being sponsored. There is nothing for your family to report.
Having the children undergo medicals does NOT mean that they will be immigrating to Canada, as they cannot do that without the father's permission or the mother having full legal custody. However, if the children undergo the medical, they can be included as non-accompanying in the mother's app, which means that they can later be sponsored by the mother is needed.
Your brother's refusal to allow his kids to undergo the medical unless his ex complies with his demands is completely selfish. The people really being hurt by his actions are the kids.