Report if you think its really worth the matter. And you dad
involved a friend? Wah... dis is really absurd... and
disturbing...
From what you describe, your family is really treading into the
'dysfunctional' line that privacy means nothing and value of family
is also suspect...
Reporting to the police is only a stop gap measure, ultimately your
family still need to have a good talk on family values and kinship
and moralities.
If I were you, I either move out (but you are 18, so you claimed
and I tink dat means you most likely be studying) or make a stand
and confront them (however you being a gal is not dat easily
acomplished compared to being a guy).
Do note: reporting to the police should be in the last of all your
options if you care for your family.