iacisrmma,
It is a nice problem to have, BH. Your children have gone to Yeshiva, and grown in their ruchniyus. They have seen their rebbeim up close and, seeing them as examples of a higher level of frumkeit (for lack of a better word), have wanted to take on their hanhogos. This is admirable up to a point. In your case, it is that their own mesorah is different. It is telling, that I have found that people follow family minhag very closely on Pesach. This is the one yomtov, that everybody comes home. We don’t see our Rebbeim at their Sedorim, and their hanhogos with mitzvas matzoh, for example. In Belz, if I’m not mistaken, bochurim of a certain age go to the Rebbe for leil haseder, for exactly this reason – the other way around.
I have an interesting anecdote on this subject, which may help. In the Mir, I had a connection with Rav Binyomin Carlebach Shlit”a. He is a son-in-law of Rav Beinish Finkel ztzvk”l, but also happens to be the grandson of my grandfather’s rebbe in Hamburg, Germany, Rav Yosef Zvi (Jozef Hirsch) Carlebach ztzvk”l. I had occasion, at least twice, to ask him what my family’s minhag is where I had doubt. (One of the questions happened to be whether we always stand for kiddush and havdolo.)
Perhaps you could find a Rebbe in your sons’ yeshivos who is of your mesora to guide them along.