Right my theory now...
Monique is the neice of the mayor, who is also the daughter of Alan and Sylvie.
They abducted Ollie for her and she's been raising him. They faked his death in the house in the hope that if anyone found out they would believe Alan/sylvie killed him but he's been living just fine ever since right in CDB.
Monique wanted another child - so slept with Tony, as she wanted a blood sibling to Ollie.
C'mon people - what are the holes in this theory?