Who are Isaiah and Elena from Frostbite and what is their importance?

Isaiah and Elena are the two Strigoi vampires that kidnap Rose, Christian, Mason, Mia, and Eddie in Spokane. Isaiah is clearly an older vampire, one who is very strong due to the length of time he has been Strigoi and from drinking large volumes of Moroi blood. Rose suspects that Isaiah was once a Moroi because of his knowledge of the royal Moroi families and his appearance. Elena is a younger Strigoi who has clearly only become Strigoi recently. Elena's appearance suggests that she was human before becoming Strigoi.