He is a PR and he included those kids in his own application.
@armoured
Okay, I don't have a perfect answer here but will try to explain what I
think matters here. Also I don't claim to have perfect knowledge so input from others would be helpful.
First, on the generic IMM0008, you need to keep in mind that this form is used for all applications, including non-family/non-spousal sponsorship. Meaning for example someone applying under an economic stream (express entry for example) would need to apply here as the principal applicant, and would include their spouse and children. Because both spouses are applying for immigration, BOTH would absolutely need to include their respective dependents (joint and previous marriages- so conceivably from even three or more previous marriages).
BUT: it's clear in the form that if it's spousal sponsorship, ONE of the spouses - the sponsor - must be a PR or citizen and therefore cannot be included in the form. Also any CURRENT PRs or citizens - for example if the sponsor's children are citizens (for example by descent or birth) - they should not be included.
This case is a bit different because his children from previous marriage are NOT your dependents. Also it seems that the former spouse has full legal custody (they may technically not be dependents of your spouse, either), but that's a legal question; your spouse though SHOULD have specific documentation on this to answer these related questions.
And because he's not an applicant in the generic application, I don't think they need to be included in your application (although they are children of spouse, they're not dependents of the applicant or other applicants by chain). (By way of example, there are specific instructions about dependents of dependents - e.g if you had 18 year old children with their own children - they are included by 'chain.')
So I _think_ in this case you do not include because they are not your dependents. Further it's helpful here that he previously applied and included them in his application as (I presume) non-accompanying.
So my suggestion is: do not include but provide a short letter of explanation that they are not your dependents, they were previously examined in your spouse's application (provide copies of documents if possible) with the requisite non-accompanying waivers, etc. I would think/hope this is more than sufficient for IRCC. Hopefully in this case the 'worst' is that IRCC may ask for more documentation (but hopefully not).
Important qualifications/caveats: you say the children do not wish to cooperate. Common sense is that your spouse should reach out to them and let them know - depending on certain specific legal interpretations, this might mean they could never be sponsored to Canada. (Why rule that out? Apart from going for a medical examination, it's a zero-cost option). The other main qualification is I'm guessing at custody and related points, I don't actually know these things. If the spouse has zero contact with these children and has no custody and it's all settled, that may mean one set of conclusions. If it's more complicated (and it almost always is more complicated), it is worth considering the services of a lawyer, particularly if there is any chance that your spouse may wish in future to reestablish relations or account for potential future changes.
Worth noting though that for the older children - the 22 year old can't, I think, be sponsored at all, and for the 21 year old, the window will close soon (at 22 years of age). Perhaps your spouse and his ex-spouse will want to approach differently for the 17 year old.
