Hello and sorry for the late reply,
"upgrading milking parlor" : increases the milk output from milking fapets in that specific milking parlor (the volume poured into the bucket is greater), and the look also changes :)
"the second chapter require me to buy it again even though I already bought the first chapter" : most likely yes, it'll either be as a DLC or a separate game (most likely). To be clear, the second chapter won't be released this (2023) year, i don't have any estimate date in case others are wondering, sorry T^T