Heya Annwfn! If you'd like, you can convert the set to 48x48 for use in MV. I know it's a ton of work since each tile would most likely need to basically be redrawn depending on complexity. I really appreciate the fact that you're willing to send me the results of your effort. So definitely go for it if you feel up to it! : D
Viewing post in Can I Convert it to 48x48 dimension for MV?
This made me think that maybe it's doable via machine learning. Upscale the image to high resolution with super resolution technology, like waifu2x, then pixelate it back to 48x48 with something like https://github.com/sedthh/pyxelate.
I've never tried such process, don't know if it works. But it's certainly better than simply up-scaling the image. But still, redrawing is unavoidable for the best quality.