Q. Grandparents visiting their children in Israel for Peisach, should they be joined by the children and grandchildren on the second seider so the grandparents can comply with the mitzva of vehigadta levincho, even when they only keep one day?

A. Teshuvos Vehanhogos (4: 102: 2) reasons that just as when there is no children present at the seder, one complies with this mitzva by telling the story to his wife, (P’sachim 116), although she is exempt from this mitzva herself (Rambam Avoda Zarah 12: 3), so too one would comply by telling it to his children or grandchildren who are also exempt since they keep only one day. He debates that the Halacha status of the wife may be different since even if she is exempt of this positive time dependent mitzva, she can still voluntarily accept it and if there is a bracha to be recited she can do so, which is not the case of the children in the second day since they are totally exempt.
He then concludes that that it is likely that the grand parent does comply with the mitzva, since it is mainly on him, regardless of to whom he tells the story of Yetzias Mitzraim.
He compares it to a similar question in regards to a distinguished talmid of the Brisker Rov zt”l visiting Eretz Yisroel, who came to pay his respect to his his rebbe on the last day of YomTov. The day was for the Brisker Rov already Issru Chag, while for the visitor trying to comply with the mitzva of honoring his master, it was still YomTov.
Horav Yitzchak Berkovits Shlit”a told me that Horav Eliashuv zt”l, ruled that children living in Eretz Yisroel are not obligated to partake in the second seder of visiting parents, if they find that difficult.
Horav Shlomo Miller’s Shlit”a pointed out to the Rambam (H. Chometz Umatzo 7: 1) that the mitzva is to relate the miracles and wonders that happened to our forefathers… as it says: Remember this day that you went out of Mitzraim, and it says: Remember the day of Shabbos to sanctify it. As mentioned above the mitzva is telling the story even to ourselves, similar to remembering Shabbos. So if the children or grandchildren are not present he complies with the mitzva also.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a