TRV application refused for my spouse and kids

[Simone B]

I have been studying in Canada since September 2017. My spouse recently applied for TRVs for my two children and himself to spend the christmas holidays with me. All three application were denied. Just wondering how soon can they reapply and how can my spouse establish stronger ties to our home country(since that was one of the basis on which they were denied)? Is it true that internation students cannot invite any friends or family unless they have been enrolled in school for at least six months?