You are certainly wise and caring by asking for advice before you go home in order to plan ahead correctly so that you and your family will maintain maximum harmony and you personally will be able to fulfill the mitzvah of honoring your parents in the best way possible.
You should let them know in advance which kashrut symbols you consider as being kosher. It is also appropriate to offer to do the shopping so as to save your parents the efforts involved in finding kosher products and to insure the kashrut of the food. I also suggest that you offer to help with the food preparation (both physically and financially), since your special request is likely to be the cause of added effort and expense.
A person should keep in mind regarding the Torah, “Its ways are ways of pleasantness and all its paths are peace” (Prov. 3:17). If a person’s actions do not bring peace, very often this may be due to the fact that he is not following the ways of the Torah which require him to act respectfully toward his parents, to pursue peace, and to be sensitive to the wishes of other people.
