They are all avoidable. Just do not pursue a romance of any of the companion characters. To pursue romance you choose the dialogue option that has a heart icon. So don't choose those, you won't see anything.
But there is no way to prevent them from being available if you choose that option (they can't be removed or filtered). So it is up to you not to choose those options. Note there is a lot of frank talk about sex, plus innuendo that is unavoidable due to playing as banter while wandering around. This is mostly with Dorian, Iron Bull and Sera, so I suppose you could not take those companions with you, and avoid talking to them at your base.
But yes, your parents would have to purchase the game, so they should be aware.