I think the only thing we need to work out now is where they live. They can be living on their own or in Michi's parent's home since it's close to the academy. Either way Michi wouldn't mind. In the case of Michi's home Oliver could have one of the rooms that used to belong to her older brothers.

Edit: Also I forgot to mention that her mother (Nana) is her father's (Hideaki) weapon. Nana's weapon form is a spear.