I am not going to lie, I didn't really read the "horde killing" and "inspired by Vampire Survivors" part, so the part that came after killing your sister came as quite a shock (in a good way)! The gameplay is very crisp and responsive, taking the Vampire Survivors concept from 2D to 3D was an awesome idea, and the leveling system was a delight to explore, with all the different vegetables and recipes!
Of course, the artstyle and the plot really ties it all together, tying a hardcore action gameplay with a somber and fatalist narrative. The two didn't feel like they would mix, but you really excelled at it!
This is just a personal reading, but I didn't quite realize that you keep playing as one mouse. I thought that if you fail, you kill the eldest sister, and then you become the elder sister that is destined to be killed. And the idea of this roguelite that still has a risk factor (albeit an emotional one) is stellar. If you cannot beat Mother of Many in this run, nothing happens to you the player, but you know that you allow this cycle to continue and resulted in a death of yet another sister. That is such a gut punch, and really incentivizes the player to beat the game as quickly as possible.
I know this reading doesn't seem to be the correct one, judging by the ending, you always played as one mouse, but I don't know whether this was influenced by an artistic choice or time constraints on the project. The theme of incremental progression of a society to elevate oneself above a cruel deity and a backwards ritual is a theme that really shines within your project.
Apologies for the long message, I just wanted to tell you just how much I loved your folks' work. Thank you so much for making this game and wish you all the best in your future projects!