I know a woman who is on her way towards Geirus soon. The rest of her immediate family will not be converting , Just she herself. Since a yid cannot cook for a goy on yom tov, so therefore , after her conversion , will there be any heter for her to cook for her own family, since they havent converted ? Wouldnt disallowing this lead to significant lack of simchas yom Tov for her if she cannot feed her children ?
In general, a Jew cannot cook or do other melacha related acts for a gentile on Yom Tov. The reason is because we are permitted to cook on Yom Tov only if it is for the honor of celebrating the Yom Tov. Since gentiles are not included in the Yom Tov, (or non or non-observant Jews, who aren’t observing the Yom Tov) cooking for them is not considered doing melacha for the purpose of the Yom Tov. The Shulchan Aruch (Orach Chaim 512-1) states that the added precaution of not inviting such a guest is only for a prominent person, when the hostess might cook an additional dish in honor of the guest. However, however a person may add extra food to a pot for their servant’s. The reason for this is because merely adding extra food to a pot is not doing any additional melacha, as putting the pot on the fire is the same one action for all the food together. Additionally, since they are his servants, there is no suspicion that the person will cook a special dish for them.
A person’s young children, who live in the home, would not be considered “guest”, as they are not invited specially, and they aren’t prominent enough, that we ae afraid that the mother will make a special dish for them, rather, they will eat from the food that was cooked for the family.
Therefore, what is best is that she should cook everything before Yom Tov. Then on Yom Tov, when she will serve her meal, she is only reheating the food, which is not doing any extra melacha for each portion. For example, if she is putting up a roast to cook, she isn’t adding melacha for her children, and that would be allowed, however when frying cutlets, there is melacha done for each one, which would not be permitted. Yes, it is a bit tricky, but it is doable, and she can manage fine.
It should be noted that this is only meant to be a general answer, and if she has any specific question, she should speak to her Rov.