Gatolic here; I come from a household which was split in the middle due to my father and his family being hardline Stalinists.
I would suggest:
1) pray for them, and thank God for entrusting them with a father who cares for their soul;
2) be patient and gentle, don’t come in as being forceful: it takes patience and time for the seed to grow into a tree;
3) buy them a prayer book and other books which could shine some light on why you begum Ortho;
My father came to the faith in his late 30s, and he still has issues with many things…but without my mother’s silent prayer and work, without her patient example he would have stayed a Communist. Your children at least already have some of the fundamentals of what Christian faith is, so if you have the patience and love to show them the whys of you finding Christ in the Orthodox Church, they could follow you.