for those still desiring a walkthrough for this, I've found that the main choices for the game boil down this
1st choice: spend time with wife
2nd choice: sex with wife
3rd choice: spend time with sister-in-law
4th choice: sex with sister-in-law
I have gotten all the h-cgs, all the scenes/endings, and all but one of the non-h cgs.
I have found 4 different endings: 1 unhappy (atleast i think it was unhappy, half the time I can't follow the conversations even with english), 1 happy with wife, 1 happy with sis-in-law, and one happy with both.
for the unhappy, choose the first option till it disappears, then choose the third option until the game ends
for the wife ending, choose the second option till it disappears then choose the first till the game ends
for the sis-in-law ending, choose the fourth option till it disappears then choose the third till the game ends
for both, alternate between the second and fourth choices until the game ends
for the decision trees with only two decisions, I have yet to determine if they really affect the outcome aside from minor details in the story and alternate cgs... and the only one I can say for sure might have an affect is at the zoo, where you choose to either visit the monkeys with your wife or the chimps with her sister.
I will freely admit that it got to the point that I began skipping large chunks of dialog because I could not figure out what the hell was going on in that conversation.
sorry it's so long winded, put it in spoilers so those who want to do it on their own can bypass it easily