To have theese scenes, well you probably noticed their bellies and collars. It explains almost all you have to do.
You just need to follow Hints about Bree and Sasha until they are seduced then impregnate both hers, don't forget the collars and maybe buy hers some piercings. And once they are both pregnant you'll run into an "argue" with Sasha and Bree (especially with Sasha...) and I guess if hers kink/love are high enough girls are furious but stay with you anyway.
The only small problem I had was with Bree last part. The Hint said "I should visit her in her bedroom when she is at home". Then I must have done it at least 20 times without success and I was about to quit (and miss theese wonderful scenes!) until I go in the street where I met Bree and which triggered Bree last part.