Impressive work!!!
I saw in the comments that you are using software sprites and a sprite multiplexer for hardware sprites. Coder LFT made two sprite routines that I think could be usable in the game of this type:
https://www.linusakesson.net/programming/fieldsort/index.php
https://www.linusakesson.net/scene/lunatico/misc.php
If you have the time, take a look, it may be something that could be useful to you. I really hope that this game will be finished.
Cheers!