Actually I didn't drink the milk at all I collected it up until I had all of it and if I recall it was a total of two or three but I never saw what the second key was for or that chest in the hedge maze
honestly it depends on what games are compatible with joiplay like you need the rpg maker player and a specific version for your game to run but joiplay has add-ons that i installed to get it working and I suggested looking up a guide on joiplay if you want to play certain PC games on your android phone if you got one