You mentioned that script is finished, so it's request for Your next projects, do not add pregnancy in last part of a game, let female MC to get pregnant in the middle or first third part of story.
Instead of pregnancy ending (hate them), better to show reaction of female MC, anger, hate, disgust, degeneracy of being impregnated by some small inhuman creature. Scenes where she lies to people asking who is a father, dialog after giving birth with her saying it's definitely won't happen again, etc.
Also You mentioned body changing with corruption, sounds great, adding her angry reactions on her body becoming more suitable for breeding would be good. And what about her nipples darkening when (if) she'll get pregnant, also will You add lactation?
P.S. One thought about ntr, Yennefer is quite bitchy ambitious character (at least in the books), she's ready to lie and fuck if it can benefit her or witches' circle, she never committed herself to anyone, while Geralt is wandering philosopher who never heard about monogamy.
And goblin can't be ntred cause he's not loving her but wants to turn her into breeding bitch.
P.P.S. Also last remark, Yennefer is a witch and lives for couple hundreds of years, books don't cover her whole life, so you all can consider this story a canon, with inexperienced witch Yennefer spending several years as goblin's baby-making machine before she found way to escape.