Yes, there are also special events at least for Ririko+Kotone and Ririko+Saya, so perhaps there is one for Kotone+Saya as well. Keep in mind if you want to get all 3 pregnant then you'll prolly need to use the guide someone posted earlier or plan things out really well, also I think Saya has a mechanic where if you get her pregnant there's only a certain number of days before her ending starts forcibly even if it's not day 35 yet. The trick is advancing the stories for everyone you wanna impregnate right up to the point where you can start doing it by getting special events and to go for them in order of least blockage while they have an egg, for example if you start Ririko's penultimate events during the thug arc with Saya her egg will be gone before you can finish impregnating her and you'll need to spend extra time to do her unless you to the dual Ririko+Saya scene where both get pregnant.
Also keep in mind you can keep an egg going by making one of the girls ovulate while a previous one is still active with certain scenes. This is mostly relevant to Kotone since that way you can retain your progress on her relatively easily. The guide has several NTR events that should be avoidable while still getting the harem end if things are timed slightly differently (more time for the setup to prevent NTR, starting on the end spurt later, doing the thug arc). Also keep in mind you can get an extra event with Yukino by choosing to "take care of [her]" at midnight instead of resting.
BlueArcher Do the Yukino event at day 28 midnight instead of resting and she'll appear.
