Two options in my opinion.
First one is to redesign the mold to have only 2 parts that are 2 semi shells, the way you desing it currently need to have a very strict tolerance in the parts which I don’t think are doable with a 3d printer (also, the wall seems too little thick). With a 2 part mold, you do some holes for the water on what will be the back side of your tile and you should be good.
Another option is to use something different, like white wall gypsum and maybe adding some acrylic color it needed, and somewhat copy the way the real tile are done.
If what you are doing is for model and/or some game, white gypsum is great, I did some nice diorama for aircraft with them. And it is more durable in my opinion.
Got it. I did’t consider the extraction.
Not if it work well.
If they endure the pressure they are ok. I would have done them thicker but just to be sure.
For the gypsym it seems strange, every time that I did something with it I had no problem to remove from the mold, expecially if it was made with some sort of plastic. Probably more than the pieces you need to sand the mold to have smooth surfaces, so that the gypsum does not adhere to it.