Hi Eladio
You have a mathematical mind! Congratulations! In addition to what CalifJim and MrP have said, I would like to add a couple of comments. In one of your sentences not is in the wrong place:
"Shall not we ever get used to this house?"
Not can't be after a defective/modal auxiliary (shall) in a negative question unless it is contracted (shan't). Say:
Shall/will we not ever get used to this house? Or, better still:
Shan't/won't we ever get used to this house? / Shall/will we never get used to this house?
Secondly, used to need not indicate habitual action in the past. It is frequently used with verbs such as live and like:
He used to live here when he was a teenager.
The meaning is the same as: He lived here when he was a teenager.
Another example: I used to like the way she dressed in those days.
Cheers
CB