Have the player open the save file and look into the player data for another data besides the player's own data and delete the other player data or look up the other player's data on namemc by copying the player data to look up the uuid to know who joined in your worlds.
Minecraft should have a no lagging game and that the all the versions in minecraft working together since i never seen that and that minecraft should add custom models and that minecraft should include more shapes and insects and animals and more animations on the models