I'll talk about it later

Both MC and William's parents were born.

MC's parents: 1985 (both)
William's parents: 1987 (dad) 1988 (mom)

Fun fact: James Miller is Charles Miller's younger brother

Their father is Seamus Miller and their mother is Marie McFadden.

On the maternal side, MC's grandparents are Daniel May and Margaret Hill.
William's is Eugene Lambert and Carole Proulx.

They also have Joseph Miller, Jessica Miller, Blake Miller and Walter Miller as their siblings.
On the mother's side, MC's aunt and uncle's are Edith May, Chris May and Alexander May.
William's is Jean-François Lambert and Jennifer Lambert.

What about CC's parents?
They were born in 1983 (dad) and 1986 (mom)