unfortunately the best option is probably to draw that stuff natively at 48px.
interesting thing tho, you don't have to stick to 48x48 for charsets, you'll just have to deal with having a 48x48 size hitbox, which honestly isn't that bad if you're parallax mapping.
fortunately parallax mapping is soooo much easier in mv/mz than the previous makers, just slap a ! at the beginning of your parallax background's file name and it'll have proper scrolling for parallax mapping. You'll have to place the collisions yourself though. I suggest using the two tileset method, where you map with one that shows the x's and o's and then swap to an invisible version during gameplay.
