Depends on the wish. My Mom told me as the oldest son that I will need to see to the details of her funeral one day, and that she wants to be cremated. I told her I would not comply because Jews do not cremate themselves, it is against our way [Jews are buried in no-frills inexpensive pine boxes]. She agreed with my view and changed her wishes. She said she wants a few carnations at her funeral because that is her favorite flower. Flowers are against tradition but I said, "yes, of course", because that's what she wants and there is no real harm or law against flowers [donations in the name of the deceased are more traditional because their benevolence continues to live on, while flowers die and add death to the death.].
There are different views on the halakcha of organ donation, or donating one's body for science. Some Rabbis say yes [if the idea is to save a life as one's last act], others no. I would ask your family member's Rabbi, or your Rabbi, for the halakcha on this if you need an answer. It's a good question to raise.
I think it's better, and more moral, to disappoint a family member than break halakcha [especially at the end of life, why attach sin to a departing soul?].
