Here's a clarafication on the families so that it won't be so confusing.

JongKyung family = Dabin (23), Taeyeon & Heechul (17)
Key family = 2 boys (10 & 7)
Onew family= 1 girl (15)
Minho family= 1 girl (13), 1 boy (7)
Taemin family= 1 boy (3)
Minhyuk family = 2 boys (15, 13), 1 girl (2)

The number is kid's age. As for now, I have no names for the other children but if you have any good names for the kids, please do tell me.

Dabin has five appas (Key, Onew, Minho, Taemin, Jonghyun) [Refer to the early story]. Even though she's old, she is still consider to be daughter of all five of them even when they have their own children. Heechul & Taeyeon on the other hand are their nephew and niece. Therefore the twins call SHINee, uncles except for Dabin.

Hope this helps answer some of your questions. ^^