No, you can not MAKE them observe pardah, but SUGGEST to them in the light of Quran and Hadith. If they were Muslims and believe in the words of Quran, they would follow.
My mother doesn't. My cousin's don't.
My grandparents are too old. But i dont think they do either.
So they aren't muslims because they choose not to wear?
And dubatta is different story. Hijab is what im talking about since that is what hadith and quran are talking about.