I am Russian national and I have an F-1 visa. My husband is a compatriot who has an F-4 visa. Currently, I am remarried and have two children aged 14 and 17 from my first marriage. My children also live in Korea, but they are not compatriots, so they enter Korea on a C-3 visa and then return back to Russia within every three months. Is there any way for my children to receive a long-term visa?