Batman Beyond: the Return of Joker?

in this movie it talks about how joker died and how harley fall and her body never found. but we realized that she lived and that she had a family and the DeeDee's were her grandchildren. My question is the DeeDees actually the jokers grandchildern or what??? I know that in the gang they called him uncle j but is the DeeDees blood related to him. This has been bothering me and i need to know. Please no smart a$$ comments. I just want someones opinion on this.