When dev will add point system in this game, even without walktrough it will be clear enough
For mom you need to be gentleman, caring son and man. Fpr sis you need to be confident, rude douchebag.
One of the scenes to consider is peeping on mom and then doing dishes by ourself. That way we will get wine to steam up our nightly cuddling with mom. To sis you need to be rude, fight with her even, accuse and put her under pressure. Buy weed, i bought for 40$, see her in panties, see her stretching and slap her ass, put her under pressure on family dinner but if there is possible compliment, remember to say it etc. If you want to get closer with mom, you need to be nice and caring. Be a dick and you will die, literally.