I play windows 20.05.09 version here so please forgive me if these bugs are already fixed.
1. At some point in the game I somehow just couldn't impregnate anyone anymore no matter how many times I tried. So I couldn't get wyvern girl pregnant for hellhound village.
2. I already have 100 relation with water lamia and gave her water shield but still couldn't unlock her sex scene. Every time I talked or pet her she just gave me more scale.
1. For all girls outside of your party, the impregnation is based on a randomly generated number. It's possible to get girls pregnant when replaying scenes from the CG room, but sometimes it may take a while when you're unlucky. ;)
2. The water lamia, raijuu and cowgirl monstergirls have no CG scenes yet.