What is the ruling on one who spends on their parents while their siblings sell the furniture, furnishings, and food items sent and purchased for them, and should they stop the expenditure, knowing that their goal is the pleasure of Allah and then the pleasure of their parents?

If your parents are in need, spending on them is a righteous deed, and it is obligatory upon you if your siblings do not spend on them and you are capable of doing so. If your siblings dispose of your parents' money without permission, they are transgressors, and you must admonish them. However, this does not justify your refusal to spend on your parents when they are in need.