I want to shift to my elder son’s house as I am staying alone with my younger bachelor son and facing health problems due to non-availability of healthy food. But my elder son is staying with his girlfriend and they are not married. I will be given my separate bedroom but will have to eat food made by her. I am not sure if they are taking care of Ghusl also. My son and his girlfriend are Ismaili Khoja
Kindly advise if I can stay with them and eat food made by her from the Tahaarat point of view

There is no objection to housing and eating as long as the food is permissible, and you must advise them to marry, and that they are committing major sins that necessitate entering Hellfire.