Hi, programmer here!
I am interested on this game project as I already have experience coding undertale-like battle system. However, I don't use GameMaker so I cannot help you. Sorry.
I hope you find someone who can help you
well I hope you find someone or some people youself, though unsure why you commented then? But good luck!
I mentioned it because I genuinely like your project idea and, if you ever change the requirements about the game engine, you know where to find me :)
oh ok :
