How can I honor my parents despite the difficulties I face, such as stress and shouting at them, and the difficulty of fulfilling their requests, especially concerning frequent visits to my grandfather? And is honoring them limited to only obeying their commands?

Raising one's voice at parents contradicts filial piety, and obedience to them is obligatory in matters that do not involve disobedience (to Allah), and in what benefits them without harming the children. This is true even if it is difficult for the children, as long as they are not harmed. However, if there is harm, then obedience is not obligatory, but one must apologize to them gently and respectfully. Filial piety is among the best deeds and the most beloved to Allah.