How do you unlock the 3P skill?

[Demi-Goat]

I can't seem to figure out how to actually get the 3P and 4P skill. THey are displayed in the skill menu, but I can't buy them. I have 100 affection with all 3 girls. What am I missing?

[[MOE]Lt.CaTZiLa]

FOR 3P
You have to do H with Yui or Rio in the room with Silence skill off and keep doing
the girls you didn't do H with [Rio or Yui] need to have high vigilance point (around 60-70 is best) to get caught by her and join H
also need low vigilance point on Miyuki and uncle [or you will get caught and game over] (I already try to do with Miyuki but it not work some how and game overX

For 4P
Same deal but you do 3P with Yui and Rio and get caught by Miyuki