From what I can gather from changelog there are two impregnable girls - Rada and Sveta (or Glad and Light, if you prefer google-speak), and Rada is probably a netore content (you cuck someone else). Maybe you can breed Persians (cats?)
You can also impregnate Marina (Antonina's daughter that works at the Mall; knocking her up sort of removes her from the game, at least temporarily, as her mom sends her away to give birth), and Aunt Nina. (I think it used to be if you shot a baby in her and asked her to get an abortion she shunned you and her path closed off, but I think no you can just say, "J/K let's be parents" and continue on.)
There are a few other characters that have creampie finishes (off the top of my head: Dasha, Antonina, Anastasia, Elsa, Irina, Melissa, Yana, I think Luda and Masha, and of course Mom [who can also be creamed by Shurik, so your best friend might father your youngest sibling!]), so there are potential avenues for more of that kind of content (obviously with different character models).
