Can't increase throuple acceptance? Either one or the other gets off and the acceptance score doesn't go up, only jealousy
The trick is that both of them have to get off in each session and you only have 5 actions.
So you need to not kiss / caress either of them and get down to business by stroking them to hardness and the hj/bj/fuck for both of them to cum.
As the acceptance rises, you will be able to unlock more actions and threesome ones too.
Hope I got it right.