(TMZ) -- Nick Carter and his family will honor their father's dying wishes -- cremate him and spread his ashes, but the family's also decided to involve their late sister.

TMZ was told Bob -- whom the families believe died from a heart attack -- requested cremation. He wanted his ashes spread in the Gulf of Mexico by the Florida Keys.

The family would like a ceremony which reunites Bob with his late daughter postmortem. Nick's sister Leslie died suddenly at 25 back in 2012 of an overdose. Sources say she was cremated and her husband has retained her ashes ever since. 

Now that Bob died, the family would like to spread both his and Leslie's ashes at the same time. TMZ was told Leslie's husband is on board so it's all systems go.

The private ceremony will go down later this year.